Data sending method, data receiving method, network device, and terminal device

ABSTRACT

This application provides a data sending method, a data receiving method, a network device, and a terminal device, to obtain a diversity gain to a greater extent, improve received signal quality, and improve data transmission reliability. The method includes: performing, by a network device, transmit diversity preprocessing on one modulated symbol stream to obtain at least one transmit diversity spatial stream; performing, by the network device, precoder cycling on the at least one transmit diversity spatial stream to obtain at least one precoded data stream, where each of the at least one transmit diversity spatial stream corresponds to at least two different precoding vectors; and sending, by the network device, the at least one precoded data stream to a first terminal device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2018/082334, filed on Apr. 9, 2018, which claims priority toChinese Patent Application No. 201710282820.8, filed on Apr. 26, 2017.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the communications field, and morespecifically, to a data sending method, a data receiving method, anetwork device, and a terminal device.

BACKGROUND

In a long term evolution (LTE) system and an LTE advanced (LTE-A)system, a multiple-antenna technology is increasingly used for datatransmission. A multiple-input multiple-output (MIMO) technologyindicates that a transmit end device uses a plurality of transmitantennas to transmit signals and a receive end device uses a pluralityof receive antennas to receive signals.

A MIMO system usually uses a precoding technology to improve a channel.However, when channel state information (CSI) cannot be obtained becausea channel environment rapidly changes or the like, a relatively accurateprecoding matrix cannot be obtained. Consequently, a to-be-transmittedsignal obtained through precoding processing cannot accurately adapt toa current channel, and received signal quality is reduced.

Therefore, it is desirable to provide a transmission scheme to improvereceived signal quality and improve data transmission reliability.

SUMMARY

This application provides a data sending method, a data receivingmethod, a network device, and a terminal device, to obtain a diversitygain to a greater extent, improve received signal quality, and improvedata transmission reliability.

According to a first aspect, a data sending method is provided,including:

performing, by a network device, transmit diversity preprocessing on onemodulated symbol stream to obtain at least one transmit diversityspatial stream;

performing, by the network device, precoder cycling on the at least onetransmit diversity spatial stream to obtain at least one precoded datastream, where each of the at least one transmit diversity spatial streamcorresponds to at least two different precoding vectors; and sending, bythe network device, the at least one precoded data stream to a firstterminal device.

In this application, the foregoing transmission scheme may be referredto as precoder cycling based transmit diversity. However, it should beunderstood that the name is defined for ease of description anddifferentiation from another transmission scheme, and should notconstitute any limitation on this application. This application does notexclude a possibility of defining the transmission scheme by usinganother name or replacing the name with another name in a futureprotocol.

It should be noted herein that each of the at least one transmitdiversity spatial stream corresponds to the at least two differentprecoding vectors. In other words, the network device precodes each ofthe at least one transmit diversity spatial stream by using the at leasttwo different precoding vectors. For brevity, descriptions of same orsimilar cases are omitted below.

Therefore, transmit diversity preprocessing is performed beforeprecoding, so that at least a spatial diversity gain can be obtained byperforming spatial transmit diversity on an original modulated symbolstream. In addition, precoder cycling is performed on a spatial streamobtained after transmit diversity preprocessing, so that differentprecoding vectors are used for a same transmit diversity spatial stream.When a channel environment changes or a channel is inaccuratelyestimated, different precoding vectors may be used on differenttime-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. Therefore, this helps obtain transmit diversity gains in aplurality of dimensions, improves received signal quality, and improvesdata transmission reliability, so that robustness of a communicationssystem can be improved.

In one embodiment, the performing, by a network device, transmitdiversity preprocessing on one modulated symbol stream to obtain atleast one transmit diversity spatial stream includes:

performing, by the network device, layer mapping on the modulated symbolstream to obtain at least one layer-mapping spatial layer; and

performing, by the network device, a transmit diversity operation on theat least one layer-mapping spatial layer to obtain the at least onetransmit diversity spatial stream.

In one embodiment, the precoder cycling includes time-frequency resourceblock based precoder cycling, each of the at least one transmitdiversity spatial stream corresponds to one precoding vector on onetime-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.

The performing, by the network device, precoder cycling on the at leastone transmit diversity spatial stream to obtain at least one precodeddata stream includes:

performing, by the network device, time-frequency resource block basedprecoding on each of the at least one transmit diversity spatial streambased on a precoding vector corresponding to the transmit diversityspatial stream on each time-frequency resource block, to obtain the atleast one precoded data stream.

Therefore, it is relatively simple to perform a time-frequency resourceblock based precoder cycling operation, and the at least one transmitdiversity spatial stream may be precoded based on each time-frequencyresource block by using a corresponding precoding matrix.

Specifically, each of the at least one transmit diversity spatial streamcorresponds to one demodulation reference signal DMRS port on onetime-frequency resource block, each DMRS port corresponds to oneprecoding vector, and each DMRS port corresponds to different precodingvectors on any two consecutive time-frequency resource blocks.

Assuming that a quantity of the at least one transmit diversity spatialstream is x (x≥1, and x is a natural number), in other words, assumingthat there are x transmit diversity spatial streams, the x transmitdiversity spatial streams correspond to x DMRS ports on onetime-frequency resource block, and correspond to x precoding vectors; orthe x transmit diversity spatial streams correspond to one precodingmatrix, and the precoding matrix is obtained by combining x precodingvectors.

In other words, the network device performs time-frequency resourceblock based precoding on each of the at least one transmit diversityspatial stream based on the precoding vector corresponding to thetransmit diversity spatial stream on each time-frequency resource block.To be specific, the network device performs time-frequency resourceblock based precoding on the x transmit diversity spatial streams basedon the precoding matrix corresponding to the x transmit diversityspatial streams on each time-frequency resource block, and the precodingmatrix is obtained by combining the x precoding vectors.

It should be understood that the foregoing precoding matrix obtained bycombining the x precoding vectors does not indicate that the precodingmatrix is obtained by simply combining the x precoding vectors, but isobtained by combining the x precoding vectors according to a transmitdiversity rule. It should be further understood that the precodingmatrix obtained by combining the x precoding vectors is only oneimplementation, and should not constitute any limitation on this orother embodiment of the present invention. This application does notexclude a possibility that the precoding matrix includes another vector.For brevity, descriptions of same or similar cases are omitted below.

In one embodiment, the precoder cycling includes resource element (RE)based precoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.

The performing, by the network device, precoder cycling on the at leastone transmit diversity spatial stream to obtain at least one precodeddata stream includes:

performing, by the network device, RE based precoding on each of the atleast one transmit diversity spatial stream based on at least twoprecoding vectors corresponding to the transmit diversity spatial streamon each time-frequency resource block, to obtain the at least oneprecoded data stream.

In other words, a precoder cycling granularity is further refined on onetime-frequency resource block, so that the time-frequency resource blockincludes at least two REs corresponding to different precoding matrices.

Therefore, RE based precoder cycling indicates that the at least onetransmit diversity spatial stream needs to be precoded for each RE, anda finer precoding granularity is more beneficial to achieve a maximumdiversity gain.

In method 2 (further described below), a correspondence between aquantity of layer-mapping spatial layers and a quantity of DMRS portsmay be defined as any one of the following:

Definition 1: A quantity of layer-mapping spatial layers may bedifferent from a quantity of DMRS ports corresponding to thelayer-mapping spatial layers.

It is assumed that a quantity of the at least one layer-mapping spatiallayer is x (x≥1, and x is a natural number), and each layer-mappingspatial layer corresponds to y (y≥2, and y is a natural number) DMRSports on one time-frequency resource block. In this case, the xlayer-mapping spatial layers correspond to x×y DMRS ports on thetime-frequency resource block, and correspond to x×y precoding vectors;or the x layer-mapping spatial layers correspond to y precodingmatrices, and each precoding matrix is obtained by combining x precodingvectors. In other words, one layer corresponds to a plurality of DMRSports, and each DMRS port corresponds to one precoding vector.

Definition 2: A quantity of layer-mapping spatial layers may be the sameas a quantity of DMRS ports corresponding to the layer-mapping spatiallayers.

It is assumed that a quantity z of the at least one layer-mappingspatial layer is x×y (x≥1, y≥2, and x, y, and z are all naturalnumbers), and each layer-mapping spatial layer corresponds to one DMRSport on one time-frequency resource block. In this case, the x×ylayer-mapping spatial layers correspond to z DMRS ports on thetime-frequency resource block, and correspond to z precoding vectors; orthe x×y layer-mapping spatial layers correspond to y precoding matrices,and each precoding matrix is obtained by combining x precoding vectors.In other words, one layer corresponds to one DMRS port, and each DMRSport corresponds to one precoding vector.

Definition 3: A quantity of layer-mapping spatial layers may be the sameas a quantity of DMRS ports corresponding to the layer-mapping spatiallayers.

It is assumed that a quantity of the at least one layer-mapping spatiallayer is x (x≥1, and x is a natural number), each layer-mapping spatiallayer corresponds to one DMRS port on one time-frequency resource block,the x layer-mapping spatial layers correspond to x DMRS ports, and eachDMRS port corresponds to y (y≥2, and y is a natural number) precodingvectors. In this case, the x layer-mapping spatial layers correspond tox×y precoding vectors; or the x layer-mapping spatial layers correspondto y precoding matrices, and each precoding matrix is obtained bycombining x precoding vectors. In other words, one layer corresponds toone DMRS port, and one DMRS port corresponds to a plurality of precodingvectors.

In definition 1 and definition 2, each of the at least one transmitdiversity spatial stream corresponds to at least two DMRS ports on onetime-frequency resource block, and each DMRS port corresponds to oneprecoding vector. For a definition of the DMRS port, refer to adefinition of a DMRS port in an existing protocol (for example, an LTEprotocol).

In definition 3, each of the at least one transmit diversity spatialstream corresponds to one DMRS port on one RB, and each DMRS portcorresponds to at least two precoding vectors.

The definition of the DMRS port is slightly different from that of aDMRS port in a current protocol. However, this application does notexclude a possibility of modifying or supplementing the definition ofthe DMRS port in a future protocol. In this design, one DMRS may beunderstood as a group of DMRS ports defined in the current protocol, andeach group corresponds to at least two precoding vectors. In this case,for a definition of the layer, refer to a definition of a layer in anexisting protocol (for example, an LTE protocol).

It should be noted that the foregoing process of mapping a layer-mappingspatial layer to a DMRS port may specifically include: mapping thelayer-mapping spatial layer to a transmit diversity spatial stream, andthen mapping the transmit diversity spatial stream to the DMRS port,where a quantity of transmit diversity spatial streams may be the sameas a quantity of layer-mapping spatial layers.

In one embodiment, the at least one transmit diversity spatial stream isa spatial stream corresponding to the first terminal device in aplurality of spatial streams, and the plurality of spatial streamscorrespond to a plurality of terminal devices including the firstterminal device.

In other words, the network device may transmit data to the plurality ofterminal devices in a space division manner, and therefore multi-usermultiple-input multiple-output (multiple-user multiple-inputmultiple-output, MU-MIMO) is implemented.

In one embodiment, transmission schemes for the plurality of spatialstreams are the same.

In one embodiment, the plurality of spatial streams belong to at leasttwo different transmission schemes. In one embodiment, the at least twotransmission schemes include precoder cycling, transmit diversity,spatial multiplexing, or precoder cycling based transmit diversity.

Therefore, different transmission schemes may be used for datatransmission with a plurality of terminal devices, thereby increasing aspatial degree of freedom. In addition, it is possible to flexibly use aproper transmission scheme based on different channel quality, datatransmission reliability is improved, and robustness of a communicationssystem is improved.

According to a second aspect, a data receiving method is provided,including:

receiving, by a first terminal device, at least one precoded data streamsent by a network device, where the at least one precoded data stream isobtained by the network device by performing precoder cycling on atleast one transmit diversity spatial stream, the at least one transmitdiversity spatial stream is obtained by performing transmit diversitypreprocessing based on one modulated symbol stream, and each of the atleast one transmit diversity spatial stream corresponds to at least twodifferent precoding vectors; and

demodulating, by the first terminal device, the at least one precodeddata stream to obtain an estimated value of the modulated symbol stream.

Therefore, transmit diversity preprocessing is performed beforeprecoding, so that at least a spatial diversity gain can be obtained byperforming spatial transmit diversity on an original modulated symbolstream. In addition, precoder cycling is performed on a spatial streamobtained after transmit diversity preprocessing, so that differentprecoding vectors are used for a same transmit diversity spatial stream.When a channel environment changes or a channel is inaccuratelyestimated, different precoding vectors may be used on differenttime-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. Therefore, this helps obtain transmit diversity gains in aplurality of dimensions, improves received signal quality, and improvesdata transmission reliability, so that robustness of a communicationssystem can be improved.

In one embodiment, the demodulating, by the first terminal device, theat least one precoded data stream to obtain an estimated value of themodulated symbol stream includes:

obtaining, by the first terminal device, an estimated value of at leastone layer-mapping spatial layer from the at least one precoded datastream through demodulation, where the estimated value of the at leastone layer-mapping spatial layer corresponds to at least onelayer-mapping spatial layer obtained by the network device by performinglayer mapping on the modulated symbol stream; and performing, by thefirst terminal device, inverse layer mapping on the estimated value ofthe at least one layer-mapping spatial layer to obtain the estimatedvalue of the modulated symbol stream.

In one embodiment, the precoder cycling includes time-frequency resourceblock based precoder cycling, each of the at least one transmitdiversity spatial stream corresponds to one precoding vector on onetime-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.

In one embodiment, the precoder cycling includes resource element (RE)based precoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.

According to a third aspect, a data sending method is provided,including:

performing, by a first terminal device, transmit diversity preprocessingon one modulated symbol stream to obtain at least one transmit diversityspatial stream;

performing, by the first terminal device, precoder cycling on the atleast one transmit diversity spatial stream to obtain at least oneprecoded data stream, where each of the at least one transmit diversityspatial stream corresponds to at least two different precoding vectors;and

sending, by the first terminal device, the at least one precoded datastream to a network device.

In this application, the foregoing transmission scheme may be referredto as precoder cycling based transmit diversity (precoder cycling basedtransmit diversity). However, it should be understood that the name isdefined for ease of description and differentiation from anothertransmission scheme, and should not constitute any limitation on thisapplication. This application does not exclude a possibility of definingthe transmission scheme by using another name or replacing the name withanother name in a future protocol.

Therefore, transmit diversity preprocessing is performed beforeprecoding, so that at least a spatial diversity gain can be obtained byperforming spatial transmit diversity on an original modulated symbolstream. In addition, precoder cycling is performed on a spatial streamobtained after transmit diversity preprocessing, so that differentprecoding vectors are used for a same transmit diversity spatial stream.When a channel environment changes or a channel is inaccuratelyestimated, different precoding vectors may be used on differenttime-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. Therefore, this helps obtain transmit diversity gains in aplurality of dimensions, improves received signal quality, and improvesdata transmission reliability, so that robustness of a communicationssystem can be improved.

In one embodiment, the performing, by a first terminal device, transmitdiversity preprocessing on one modulated symbol stream to obtain atleast one transmit diversity spatial stream includes:

performing, by the first terminal device, layer mapping on the modulatedsymbol stream to obtain at least one layer-mapping spatial layer; and

performing, by the first terminal device, a transmit diversity operationon the at least one layer-mapping spatial layer to obtain the at leastone transmit diversity spatial stream.

In one embodiment, the precoder cycling includes time-frequency resourceblock based precoder cycling, each of the at least one transmitdiversity spatial stream corresponds to one precoding vector on onetime-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.

The performing, by the first terminal device, precoder cycling on the atleast one transmit diversity spatial stream to obtain at least oneprecoded data stream includes:

performing, by the first terminal device, time-frequency resource blockbased precoding on each of the at least one transmit diversity spatialstream based on a precoding vector corresponding to the transmitdiversity spatial stream on each time-frequency resource block, toobtain the at least one precoded data stream.

Therefore, it is relatively simple to perform a time-frequency resourceblock based precoder cycling operation, and the at least one transmitdiversity spatial stream may be precoded based on each time-frequencyresource block by using a corresponding precoding matrix.

Specifically, each of the at least one transmit diversity spatial streamcorresponds to one demodulation reference signal DMRS port on onetime-frequency resource block, each DMRS port corresponds to oneprecoding vector, and each DMRS port corresponds to different precodingvectors on any two consecutive time-frequency resource blocks.

Assuming that a quantity of the at least one transmit diversity spatialstream is x (x≥1, and x is a natural number), in other words, assumingthat there are x transmit diversity spatial streams, the x transmitdiversity spatial streams correspond to x DMRS ports on onetime-frequency resource block, and correspond to x precoding vectors; orthe x transmit diversity spatial streams correspond to one precodingmatrix, and the precoding matrix is obtained by combining x precodingvectors.

In other words, the first terminal device performs time-frequencyresource block based precoding on each of the at least one transmitdiversity spatial stream based on the precoding vector corresponding tothe transmit diversity spatial stream on each time-frequency resourceblock. To be specific, the first terminal device performs time-frequencyresource block based precoding on the x transmit diversity spatialstreams based on the precoding matrix corresponding to the x transmitdiversity spatial streams on each time-frequency resource block, and theprecoding matrix is obtained by combining the x precoding vectors.

In one embodiment, the precoder cycling includes resource element (RE)based precoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.

The performing, by the first terminal device, precoder cycling on the atleast one transmit diversity spatial stream to obtain at least oneprecoded data stream includes:

performing, by the first terminal device, RE based precoding on each ofthe at least one transmit diversity spatial stream based on at least twoprecoding vectors corresponding to the transmit diversity spatial streamon each time-frequency resource block, to obtain the at least oneprecoded data stream.

In other words, a precoder cycling granularity is further refined on onetime-frequency resource block, so that the time-frequency resource blockincludes at least two REs corresponding to different precoding matrices.

Therefore, RE based precoder cycling indicates that the at least onetransmit diversity spatial stream needs to be precoded for each RE, anda finer precoding granularity is more beneficial to achieve a maximumdiversity gain.

In this precoder cycling method, the network device may perform RE basedprecoding on each of the at least one transmit diversity spatial streambased on the at least two precoding vectors corresponding to thetransmit diversity spatial stream on each time-frequency resource block.To be specific, the network device performs RE based precoding on the xtransmit diversity spatial streams based on y precoding matricescorresponding to the x transmit diversity spatial streams on eachtime-frequency resource block, and each precoding matrix is obtained bycombining x precoding vectors.

Specifically, a correspondence between a quantity of layer-mappingspatial layers and a quantity of DMRS ports may be defined as any one ofthe following:

Definition 1: A quantity of layer-mapping spatial layers may bedifferent from a quantity of DMRS ports corresponding to thelayer-mapping spatial layers.

It is assumed that a quantity of the at least one layer-mapping spatiallayer is x (x≥1, and x is a natural number), and each layer-mappingspatial layer corresponds to y (y≥2, and y is a natural number) DMRSports on one time-frequency resource block. In this case, the xlayer-mapping spatial layers correspond to x×y DMRS ports on thetime-frequency resource block, and correspond to x×y precoding vectors;or the x layer-mapping spatial layers correspond to y precodingmatrices, and each precoding matrix is obtained by combining x precodingvectors.

Definition 2: A quantity of layer-mapping spatial layers may be the sameas a quantity of DMRS ports corresponding to the layer-mapping spatiallayers.

It is assumed that a quantity z of the at least one layer-mappingspatial layer is x×y (x≥1, y≥2, and x, y, and z are all naturalnumbers), and each layer-mapping spatial layer corresponds to one DMRSport on one time-frequency resource block. In this case, the x×ylayer-mapping spatial layers correspond to z DMRS ports on thetime-frequency resource block, and correspond to z precoding vectors; orthe x×y layer-mapping spatial layers correspond to y precoding matrices,and each precoding matrix is obtained by combining x precoding vectors.

Definition 3: A quantity of layer-mapping spatial layers may be the sameas a quantity of DMRS ports corresponding to the layer-mapping spatiallayers.

It is assumed that a quantity of the at least one layer-mapping spatiallayer is x (x≥1, and x is a natural number), each layer-mapping spatiallayer corresponds to one DMRS port on one time-frequency resource block,the x layer-mapping spatial layers correspond to x DMRS ports, and eachDMRS port corresponds to y (y≥2, and y is a natural number) precodingvectors. In this case, the x layer-mapping spatial layers correspond tox×y precoding vectors; or the x layer-mapping spatial layers correspondto y precoding matrices, and each precoding matrix is obtained bycombining x precoding vectors.

In definition 1 and definition 2, each of the at least one transmitdiversity spatial stream corresponds to at least two DMRS ports on onetime-frequency resource block, and each DMRS port corresponds to oneprecoding vector. For a definition of the DMRS port, refer to adefinition of a DMRS port in an existing protocol (for example, an LTEprotocol).

In definition 3, each of the at least one transmit diversity spatialstream corresponds to one DMRS port on one RB, and each DMRS portcorresponds to at least two precoding vectors.

The definition of the DMRS port is slightly different from that of aDMRS port in a current protocol. However, this application does notexclude a possibility of modifying or supplementing the definition ofthe DMRS port in a future protocol. In this design, one DMRS may beunderstood as a group of DMRS ports defined in the current protocol, andeach group corresponds to at least two precoding vectors. In this case,for a definition of the layer, refer to a definition of a layer in anexisting protocol (for example, an LTE protocol).

It should be noted that the foregoing process of mapping a layer-mappingspatial layer to a DMRS port may specifically include: mapping thelayer-mapping spatial layer to a transmit diversity spatial stream, andthen mapping the transmit diversity spatial stream to the DMRS port,where a quantity of transmit diversity spatial streams may be the sameas a quantity of layer-mapping spatial layers.

According to a fourth aspect, a data receiving method is provided,including:

receiving, by a network device, at least one precoded data stream sentby a first terminal device, where the at least one precoded data streamis obtained by the first terminal device by performing precoder cyclingon at least one transmit diversity spatial stream, the at least onetransmit diversity spatial stream is obtained by performing transmitdiversity preprocessing based on one modulated symbol stream, and eachof the at least one transmit diversity spatial stream corresponds to atleast two different precoding vectors; and

demodulating, by the network device, the at least one precoded datastream to obtain an estimated value of the modulated symbol stream.

Therefore, transmit diversity preprocessing is performed beforeprecoding, so that at least a spatial diversity gain can be obtained byperforming spatial transmit diversity on an original modulated symbolstream. In addition, precoder cycling is performed on a spatial streamobtained after transmit diversity preprocessing, so that differentprecoding vectors are used for a same transmit diversity spatial stream.When a channel environment changes or a channel is inaccuratelyestimated, different precoding vectors may be used on differenttime-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. Therefore, this helps obtain transmit diversity gains in aplurality of dimensions, improves received signal quality, and improvesdata transmission reliability, so that robustness of a communicationssystem can be improved.

In one embodiment, the recovering, by the network device, an estimatedvalue of the modulated symbol stream from the at least one precoded datastream includes:

obtaining, by the network device, an estimated value of at least onelayer-mapping spatial layer from the at least one precoded data streamthrough demodulation, where the estimated value of the at least onelayer-mapping spatial layer corresponds to at least one layer-mappingspatial layer obtained by the network device by performing layer mappingon the modulated symbol stream; and

performing, by the network device, inverse layer mapping on theestimated value of the at least one layer-mapping spatial layer toobtain the estimated value of the modulated symbol stream.

In one embodiment, the precoder cycling includes time-frequency resourceblock based precoder cycling, each of the at least one transmitdiversity spatial stream corresponds to one precoding vector on onetime-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.

In one embodiment, the precoder cycling includes resource element (RE)based precoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.

In one embodiment, the at least one transmit diversity spatial stream isa spatial stream corresponding to the first terminal device in aplurality of spatial streams, and the plurality of spatial streamscorrespond to a plurality of terminal devices including the firstterminal device.

In one embodiment, transmission schemes for the plurality of spatialstreams are the same.

In one embodiment, the plurality of spatial streams belong to at leasttwo transmission schemes. In one embodiment, the at least twotransmission schemes include precoder cycling, transmit diversity,spatial multiplexing, or precoder cycling based transmit diversity.

Therefore, different transmission schemes may be used for datatransmission with a plurality of terminal devices, thereby increasing aspatial degree of freedom. In addition, it is possible to flexibly use aproper transmission scheme based on different channel quality, datatransmission reliability is improved, and robustness of a communicationssystem is improved.

According to a fifth aspect, a network device is provided, and thenetwork device includes modules configured to perform the data sendingmethod according to any one of the first aspect or the possibleimplementations of the first aspect.

According to a sixth aspect, a terminal device is provided, and theterminal device includes modules configured to perform the datareceiving method according to any one of the second aspect or thepossible implementations of the second aspect.

According to a seventh aspect, a terminal device is provided, and theterminal device includes modules configured to perform the data sendingmethod according to any one of the third aspect or the possibleimplementations of the third aspect.

According to an eighth aspect, a network device is provided, and thenetwork device includes modules configured to perform the data receivingmethod according to any one of the fourth aspect or the possibleimplementations of the fourth aspect.

According to a ninth aspect, a network device is provided, including atransceiver, a processor, and a memory. The processor is configured tocontrol the transceiver to receive and send a signal, the memory isconfigured to store a computer program, and the processor is configuredto invoke the computer program from the memory and run the computerprogram, so that the network device performs the method according to anyone of the first aspect or the possible implementations of the firstaspect, or the method according to any one of the fourth aspect or thepossible implementations of the fourth aspect.

According to a tenth aspect, a terminal device is provided, including atransceiver, a processor, and a memory. The processor is configured tocontrol the transceiver to receive and send a signal, the memory isconfigured to store a computer program, and the processor is configuredto invoke the computer program from the memory and run the computerprogram, so that the terminal device performs the method according toany one of the second aspect or the possible implementations of thesecond aspect, or the method according to any one of the third aspect orthe possible implementations of the third aspect.

According to an eleventh aspect, a computer program product is provided.The computer program product includes computer program code, and whenthe computer program code is run by a network device, the network deviceis enabled to perform the method according to any one of the firstaspect or the possible implementations of the first aspect, or themethod according to any one of the fourth aspect or the possibleimplementations of the fourth aspect.

According to a twelfth aspect, a computer program product is provided.The computer program product includes computer program code, and whenthe computer program code is run by a terminal device, the terminaldevice is enabled to perform the method according to any one of thesecond aspect or the possible implementations of the second aspect, orthe method according to any one of the third aspect or the possibleimplementations of the third aspect.

According to a thirteenth aspect, a computer readable medium isprovided. The computer readable medium stores program code, and theprogram code includes an instruction used to perform the methodsaccording to any one of the first aspect to the fourth aspect, or thepossible implementations of the first aspect to the possibleimplementations of the fourth aspect.

According to a fourteenth aspect, a processing apparatus is provided,including a processor and an interface. The processor is configured toperform the methods according to any one of the first aspect to thefourth aspect, or the possible implementations of the first aspect tothe possible implementations of the fourth aspect, and related dataexchange (for example, data transmission or reception) is completedthrough the interface. In a specific implementation process, theinterface may further complete the foregoing data interaction process byusing a transceiver.

It should be understood that the processing apparatus in the fourteenthaspect may be a chip. The processor may be implemented by usinghardware, or may be implemented by using software. When the processor isimplemented by using hardware, the processor may be a logic circuit, anintegrated circuit, or the like; or when the processor is implemented byusing software, the processor may be a general-purpose processor, and isimplemented by reading software code stored in the memory. The memorymay be integrated into the processor, or may exist independently outsidethe processor.

In one embodiment, one time-frequency resource block may include atleast one of the following: a part of one resource element, one resourceelement, or a plurality of resource elements. The resource element maybe understood as a minimum scheduling unit for physical layertransmission.

By way of example but not limitation, one resource element may be oneresource block (resource block, RB). For a definition of the RB, referto an existing protocol (for example, an LTE protocol).

In one embodiment, one time-frequency resource block may include atleast one of the following: a part of one RB, one RB, or a plurality ofRBs.

In one embodiment, the transmit diversity operations include diversitymanners such as space time transmit diversity (space-time transmitdiversity, STTD, or referred to as space time block code (STBC)), aspace-frequency transmit diversity (SFTD, or referred to as spacefrequency block coding (SFBC)), a time switched transmit diversity(TSTD), frequency switched transmit diversity (FSTD), orthogonaltransmit diversity (OTD), cyclic delay diversity (CDD), and layershifting, and diversity manners obtained after derivation, evolution,and combination of the foregoing various diversity manners.

In this application, a precoder cycling based transmit diversitytransmission scheme is used to help obtain a diversity gain to a greaterextent, thereby improving received signal quality, improving datatransmission reliability, and improving robustness of a communicationssystem.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a communications system applicable to adata sending method and apparatus and a data receiving method andapparatus according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a downlink physical channel processingprocess used in an existing LTE system;

FIG. 3 is a schematic flowchart of a data transmission method accordingto an embodiment of the present invention;

FIG. 4 is a schematic diagram of time-frequency resource block basedprecoder cycling;

FIG. 5 is a schematic diagram of RE based precoder cycling;

FIG. 6 is another schematic diagram of RE based precoder cycling;

FIG. 7 is still another schematic diagram of RE based precoder cycling;

FIG. 8 is a schematic diagram in which a network device separately sendsa plurality of spatial streams to a first terminal device and a secondterminal device according to an embodiment of the present invention;

FIG. 9 is a schematic diagram in which a network device separately sendsa plurality of spatial streams to a first terminal device and a thirdterminal device according to an embodiment of the present invention;

FIG. 10 is a schematic flowchart of a data transmission method accordingto another embodiment of the present invention;

FIG. 11 is a schematic block diagram of a network device according to anembodiment of the present invention;

FIG. 12 is a schematic block diagram of a terminal device according toan embodiment of the present invention;

FIG. 13 is a schematic block diagram of a terminal device according toanother embodiment of the present invention;

FIG. 14 is a schematic block diagram of a network device according toanother embodiment of the present invention;

FIG. 15 is another schematic block diagram of a network device accordingto an embodiment of the present invention; and

FIG. 16 is another schematic block diagram of a terminal deviceaccording to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The following describes technical solutions of this application withreference to accompanying drawings.

To facilitate understanding of the embodiments of the present invention,a communications system applicable to the embodiments of the presentinvention is first described in detail with reference to FIG. 1. FIG. 1is a schematic diagram of a communications system applicable to a datatransmission method and apparatus according to an embodiment of thepresent invention. As shown in FIG. 1, the communications system 100includes a network device 102, and the network device 102 may include aplurality of antennas, such as an antenna 104, an antenna 106, anantenna 108, an antenna 110, an antenna 112, and an antenna 114. Inaddition, the network device 102 may additionally include a transmitterchain and a receiver chain. A person of ordinary skill in the art mayunderstand that the transmitter chain and the receiver chain may includea plurality of components (for example, a processor, a modulator, amultiplexer, a demodulator, a demultiplexer, or an antenna) related tosignal sending and receiving.

It should be understood that the technical solutions in this applicationmay be applied to various communications systems, such as a globalsystem for mobile communications (GSM), a code division multiple access(CDMA) system, a wideband code division multiple access (WCDMA) system,a general packet radio service (GPRS), a long term evolution (LTE)system, a long term evolution advanced (LTE-A) system, a universalmobile telecommunications system (UMTS), or a next-generationcommunications system (for example, a 5th generation (5G) communicationssystem). The 5G system may also be referred to as a new generation radioaccess technology (NR) system.

It should be understood that the network device 102 may be a basetransceiver station (BTS) in a global system for mobile communications(GSM) or code division multiple access (CDMA); or may be a NodeB (NodeB,NB) in wideband code division multiple access (WCDMA); or may be anevolved NodeB (eNB or eNodeB) in long term evolution (LTE), a relaystation, an access point, a remote radio unit (RRU), a vehicle-mounteddevice, a wearable device, and a network-side device in a future 5Gsystem, such as a transmission point (TP), a transmission receptionpoint (TRP), a base station, or a small cell device. This embodiment ofthe present invention imposes no special limitation thereto.

The network device 102 may communicate with a plurality of terminaldevices (for example, a terminal device 116 and a terminal device 122).The network device 102 may communicate with any quantity of terminaldevices similar to the terminal device 116 or the terminal device 122.

It should be understood that the terminal device 116 or the terminaldevice 122 may also be referred to as user equipment (UE), an accessterminal, a subscriber unit, a subscriber station, a mobile station, amobile console, a remote station, a remote terminal, a mobile device, auser terminal, a terminal, a wireless communications device, a useragent, or a user apparatus. The terminal device may be a station (ST) inwireless local area network (WLAN); or may be a cellular phone, acordless telephone set, a session initiation protocol (SIP) phone, awireless local loop (WLL) station, a personal digital assistant (PDA)device, a handheld device having a wireless communication function, acomputing device, another processing device connected to a wirelessmodem, a vehicle-mounted device, a wearable device, and anext-generation communications system, for example, a terminal device ina 5G network or a terminal device in a future evolved public land mobilenetwork (PLMN). This embodiment of the present invention imposes nospecial limitation thereto.

As shown in FIG. 1, the terminal device 116 communicates with theantenna 112 and the antenna 114. The antenna 112 and the antenna 114each send information to the terminal device 116 over a forward link118, and receive information from the terminal device 116 over a reverselink 120. In addition, the terminal device 122 communicates with theantenna 104 and the antenna 106. The antenna 104 and the antenna 106each send information to the terminal device 122 over a forward link124, and receive information from the terminal device 122 over a reverselink 126.

For example, in a frequency division duplex (FDD) system, the forwardlink 118 and the reverse link 120 may use different frequency bands, andthe forward link 124 and the reverse link 126 may use differentfrequency bands.

For another example, in a time division duplex (TDD) system and a fullduplex system, the forward link 118 and the reverse link 120 may use asame frequency band, and the forward link 124 and the reverse link 126may use a same frequency band.

Each antenna (or an antenna group including a plurality of antennas)and/or area designed for communication are/is referred to as a sector ofthe network device 102. For example, the antenna group may be designedto communicate with a terminal device in a sector of coverage of thenetwork device 102. In a process in which the network device 102communicates with the terminal device 116 and the terminal device 122over the forward link 118 and the forward link 124 respectively,transmit antennas of the network device 102 may improve signal-to-noiseratios of the forward link 118 and the forward link 124 throughbeamforming. In addition, when the network device 102 sends, throughbeamforming, signals to the terminal device 116 and the terminal device122 that are randomly scattered in related coverage, interference to amobile device in a neighboring cell is less than that caused when anetwork device sends signals to all terminal devices of the networkdevice by using a single antenna.

The network device 102, the terminal device 116, or the terminal device122 may be a wireless communication sending apparatus and/or a wirelesscommunication receiving apparatus. When sending data, the wirelesscommunication sending apparatus may encode the data for transmission.Specifically, the wireless communication sending apparatus may obtain(for example, generate, receive from another communications apparatus,or store in a memory) a specific quantity of data bits that need to besent to the wireless communication receiving apparatus through achannel. The data bits may be included in a transport block (or aplurality of transport blocks) of the data, and the transport block maybe segmented into a plurality of code blocks.

In addition, the communications system 100 may be a public land mobilenetwork (PLMN), a device-to-device (D2D) network, a machine-to-machine(M2M) network, or another network. FIG. 1 is merely a simplifiedschematic diagram of an example for ease of understanding. The networkmay further include another network device that is not shown in FIG. 1.

For ease of understanding of this embodiment of the present invention,the following briefly describes a downlink physical channel processingprocess in an LTE system with reference to FIG. 2. FIG. 2 is a schematicdiagram of a downlink physical channel processing process used in anexisting LTE system. A processing object of the downlink physicalchannel processing process is a code word, and the code word is usuallya bit stream that undergoes encoding (including at least channelcoding). The code word is scrambled to generate a scrambled bit stream.Modulation mapping is performed on the scrambled bit stream to obtain amodulated symbol stream. The modulated symbol stream is mapped to aplurality of layers through layer mapping. For ease of differentiationand description, in this embodiment of the present invention, a symbolstream obtained after layer mapping may be referred to as alayer-mapping spatial layer (or referred to as a layer mapping spatialstream or a layer mapping symbol stream). The layer-mapping spatiallayer is precoded to obtain a plurality of precoded data streams (orreferred to as precoded symbol streams). The precoded symbol stream ismapped to a plurality of resource elements (RE) through RE basedmapping. Then orthogonal frequency division multiplexing (OFDM)modulation is performed on these REs to generate OFDM symbol streams.Subsequently, the OFDM symbol streams are transmitted through an antennaport.

A precoding technology may mean that a to-be-transmitted signal ispreprocessed at a transmit end when a channel state is known, in otherwords, the to-be-transmitted signal is processed by using a precodingmatrix that matches a channel resource, so that a precodedto-be-transmitted signal adapts to a channel, and complexity ofeliminating inter-channel impact at a receive end is reduced. Therefore,received signal quality (for example, a signal-to-noise ratio (or Signalto Interference plus Noise Ratio, SINR)) is improved by precoding theto-be-transmitted signal. Therefore, transmission between a transmit enddevice and a plurality of receive end devices can be performed on a sametime-frequency resource by using the precoding technology, in otherwords, MU-MIMO is implemented. It should be noted that relateddescription of the precoding technology is only used as an example, andis not used to limit the protection scope of the embodiments of thepresent invention. In a specific implementation process, precoding maybe performed in another manner (for example, when a channel matrixcannot be learned of, precoding is performed by using a preset precodingmatrix or in a weighted processing manner). Specific content is notdescribed in this specification.

However, when CSI cannot be obtained because a channel environmentrapidly changes or the like, the receive end usually feeds backlong-term broadband CSI, and a precoding matrix determined based on sucha CSI feedback is inaccurate. Consequently, a precoded to-be-transmittedsignal cannot accurately adapt to a channel, and finally received signalquality is reduced. Therefore, it is desirable to provide a transmissionscheme to improve received signal quality and improve data transmissionreliability.

It should be noted herein that, in this embodiment of the presentinvention, the transmission scheme (or referred to as a transmissionmanner) may be a transmission scheme defined in an existing protocol(for example, an LTE protocol), or may be a transmission scheme definedin a related protocol in future 5G This embodiment of the presentinvention imposes no special limitation thereto. It should be understoodthat the transmission scheme may be a name of a technical solution usedfor data transmission, and should not constitute any limitation on thisembodiment of the present invention. This embodiment of the presentinvention does not exclude a possibility of replacing the transmissionscheme with another name in a future protocol.

This application provides a transmission scheme to help obtain adiversity gain to a greater extent, improve received signal quality, andimprove data transmission reliability. For ease of differentiation anddescription, the transmission scheme provided in this application may bereferred to as precoder cycling based transmit diversity. However, itshould be understood that a name of the foregoing transmission scheme isonly defined for differentiation from an existing transmission scheme,and should not constitute any limitation on this embodiment of thepresent invention. This embodiment of the present invention also doesnot exclude a possibility of replacing the name with another name in afuture protocol.

The following describes the transmission scheme in detail with referenceto the accompanying drawings.

First, the data transmission method in the embodiments of the presentinvention is described in detail with reference to FIG. 3 to FIG. 9. Itshould be understood that these examples are merely intended to help aperson skilled in the art better understand the embodiments of thepresent invention, instead of limiting the scope of the embodiments ofthe present invention. It should be understood that, if the transmit endis a network device and the receive end is a terminal device, thenetwork device may send downlink data to at least two terminal deviceson a same time-frequency resource; or if the transmit end is a terminaldevice and the receive end is a network device, at least two terminaldevices may send uplink data to one network device on a sametime-frequency resource.

Without loss of generality, the following uses an example of datatransmission between a network device and a first terminal device todescribe the data transmission method in the embodiments of the presentinvention. It should be understood that the network device maycorrespond to the network device 102 in FIG. 1, and the first terminaldevice may be any one of the plurality of terminal devices that are incommunication connection to the network device, and may correspond tothe terminal device 116 or the terminal device 122 in FIG. 1.

Particularly, it should be noted that, in the embodiments of the presentinvention, for ease of description, precoding is used for implementingspatial multiplexing when there is no special description. However, aperson skilled in the art should understand that the precoding mentionedin this specification may be described as spatial multiplexing precodingmore generally if there is no special description or if the precoding isnot in conflict with an actual function or inherent logic of theprecoding in related descriptions.

FIG. 3 is a schematic flowchart of a data transmission method 300according to an embodiment of the present invention from a perspectiveof device interaction.

Specifically, FIG. 3 shows a downlink data transmission process.

It should be noted that, in this embodiment of the present invention,one modulated symbol stream is only used as an example to describe thedata sending method. However, this should not constitute any limitationon this embodiment of the present invention. A network device mayperform transmit diversity preprocessing on a plurality of modulatedsymbol streams to obtain at least one transmit diversity spatial stream,and the network device may perform transmit diversity preprocessing onthe plurality of modulated symbol streams by using a layer mappingmethod in LTE. Without loss of generality, the following uses a processof processing one modulated symbol stream as an example to describe thisembodiment of the present invention in detail.

As shown in FIG. 3, the method 300 includes the following operations.

Operation S310. The network device performs transmit diversitypreprocessing on one modulated symbol stream to obtain at least onetransmit diversity spatial stream.

In this embodiment of the present invention, the modulated symbol streammay be a modulated symbol stream to be sent to a first terminal device.The network device may perform transmit diversity preprocessing on themodulated symbol stream to obtain the at least one transmit diversityspatial stream. The network device may perform transmit diversitypreprocessing on the modulated symbol by using a prior art. By usingSFTD as an example, layer mapping and Alamouti coding may be performedon an original modulated symbol stream to obtain at least one transmitdiversity spatial stream. However, it should be understood that theforegoing enumerated specific transmit diversity preprocessing method ismerely a possible implementation, and should not constitute anylimitation on this embodiment of the present invention. This embodimentof the present invention is also not limited thereto. For example, thenetwork device may directly obtain the at least one transmit diversityspatial stream by performing the transmit diversity preprocessingoperation on the modulated symbol stream.

It should be understood that, in this embodiment of the presentinvention, one modulated symbol stream is only used as an example todescribe the data sending method. However, this should not constituteany limitation on this embodiment of the present invention. The networkdevice may perform transmit diversity preprocessing on a plurality ofmodulated symbol streams to obtain a plurality of transmit diversityspatial streams. The network device may use a same method to performtransmit diversity preprocessing on each modulated symbol stream toobtain a transmit diversity spatial stream. In this embodiment of thepresent invention, without loss of generality, the process of processingone modulated symbol stream is used to describe this embodiment of thepresent invention in detail.

In one embodiment, operation S310 includes:

performing, by the network device, layer mapping on the modulated symbolstream to obtain at least one layer-mapping spatial layer; and

performing, by the network device, a transmit diversity operation on theat least one layer-mapping spatial layer to obtain the at least onetransmit diversity spatial stream.

For ease of understanding and differentiation, spatial streams obtainedafter different processing have different names in this application. Forexample, a spatial stream obtained after layer mapping is referred to asa layer-mapping spatial layer, a spatial stream obtained after atransmit diversity operation is referred to as a transmit diversityspatial stream, and a spatial stream obtained after precoding mentionedin the foregoing descriptions is referred to as a precoded data stream.However, a person skilled in the art should understand that variousspatial streams mentioned in this application all belong to modulatedsymbol streams. It should be further understood that names such as thelayer-mapping spatial layer, the transmit diversity spatial stream, andthe precoded data stream are defined for ease of differentiation andshould not constitute any limitation on this embodiment of the presentinvention. This application does not exclude a possibility of replacingthe foregoing names with other names in an existing protocol or a futureprotocol.

By way of example but not limitation, the transmit diversity operationmay include diversity manners such as a space time transmit diversity(STTD, or referred to as space time block code (STBC)), aspace-frequency transmit diversity (SFTD, or referred to as spacefrequency block coding (SFBC)), a time switched transmit diversity(TSTD), frequency switched transmit diversity (FSTD), an orthogonaltransmit diversity (OTD), a cyclic delay diversity (CDD), and layershifting, and diversity manners obtained after derivation, evolution,and combination of the foregoing various diversity manners.

For example, one transmit diversity spatial stream may be obtained if atransmit diversity operation is performed on one layer-mapping spatiallayer through CDD processing; and at least two transmit diversityspatial streams may be obtained if transmit diversity preprocessing isperformed on one layer-mapping spatial layer through SFTD or STTDprocessing.

For ease of understanding and description, the following uses SFTD as anexample to describe this embodiment of the present invention in detail.However, it should be understood that the following description ismerely an example, and should not constitute any limitation on thisembodiment of the present invention. Any one of the foregoing enumeratedtransmit diversity operation methods is applicable to this embodiment ofthe present invention.

By using SFTD as an example, the transmit diversity preprocessing may beunderstood as a process of performing layer mapping and Alamouti coding(in other words, space frequency block coding) on the modulated symbolstream to obtain at least two transmit diversity spatial streams, andthe process (in other words, the layer mapping and Alamouti codingprocess) may also be considered as a precoding process. However, theprecoding is obviously different from precoding used for implementingspatial multiplexing. The Alamouti coding may be understood as apossible implementation of the transmit diversity operation.Correspondingly, still by using SFTD as an example, a transmit diversitytransmission scheme in the prior art may be a transmission scheme ofperforming transmit diversity preprocessing on one modulated symbolstream to obtain at least two transmit diversity spatial streams.

If transmit diversity preprocessing performed on the modulated symbolstream is also considered as precoding, the method in this embodiment isequivalent to performing two-level precoding on the modulated symbolstream, which may be represented as Y=F₁(F₂(X)), where F₂ representstransmit-diversity-corresponding precoding (in other words, transmitdiversity preprocessing) that is used to implement transmit diversity,F₁ represents beamforming precoding that is used to implement spatialmultiplexing, and X represents a modulated symbol stream. It can beunderstood that different transmit diversity operation methods bringdifferent quantities of ports of finally sent precoded data streams. Forexample, when the transmit diversity operation method is the SFTD, thequantity of ports may be 2; or when the transmit diversity operationmethod is the FSTD, the quantity of ports may be 4.

The SFTD is used as an example. Assuming that two layer-mapping spatiallayers obtained by performing layer mapping on the original modulatedsymbol stream may be represented as

$\begin{bmatrix}s_{1} \\s_{2}\end{bmatrix},$two transmit diversity spatial streams obtained by performing a transmitdiversity operation on the two layer-mapping spatial layers may berepresented as

$\begin{bmatrix}s_{1} & {- s_{2}^{*}} \\s_{2} & s_{1}^{*}\end{bmatrix},$where s* represents a conjugate of s.

Operation S320. The network device performs precoder cycling on the atleast one transmit diversity spatial stream to obtain at least oneprecoded data stream.

After performing transmit diversity preprocessing on the modulatedsymbol stream to obtain the at least one transmit diversity spatialstream, the network device may precode the at least one transmitdiversity spatial stream to obtain the at least one precoded datastream. In this embodiment of the present invention different from theprior art, the at least one spatial stream is precoded by using aprecoder cycling method. In other words, each spatial stream is precodedby using at least two different precoding vectors.

It should be noted that each of the at least one transmit diversityspatial stream herein may correspond to at least one precoded datastream, and a quantity of precoded data streams depends on a quantity ofantenna ports.

For ease of understanding of this embodiment of the present invention, aprior-art process of precoding the at least one transmit diversityspatial stream obtained after transmit diversity preprocessing isbriefly described first.

The SFTD is still used as an example. The at least one transmitdiversity spatial stream obtained after transmit diversity preprocessingmay be x (x≥2, and x is a natural number) spatial streams. It is assumedthat x is equal to 2, two transmit signals of the transmit diversityspatial streams obtained by performing transmit diversity preprocessingon the modulated symbol stream may be as follows:

${S = \begin{bmatrix}s_{1} & {- s_{2}^{*}} \\s_{2} & s_{1}^{*}\end{bmatrix}},$where

s* represents a conjugate of s, [s₁−s₂*] represents one stream, and[s₁−s₂*]represents another stream.

The signals are precoded to obtain the following precoded data stream:

${{WS} = {\lbrack {w_{1}\mspace{14mu} w_{2}} \rbrack\begin{bmatrix}s_{1} & {- s_{2}^{*}} \\s_{2} & s_{1}^{*}\end{bmatrix}}},$where

W=[w₁ w₂] is a precoding matrix. It can be learned that different datastreams are precoded by using different precoding vectors. The at leastone transmit diversity spatial stream obtained after transmit diversitypreprocessing is precoded to obtain the at least one precoded datastream.

In this embodiment of the present invention, the at least one transmitdiversity spatial stream is precoded by using a precoder cycling method.To be specific, there are at least two precoding vectors used to precodeany one of the at least one transmit diversity spatial stream. In otherwords, there are at least two equivalent channel matrices correspondingto each spatial stream.

Specifically, the precoder cycling may be classified into time-frequencyresource block based precoder cycling and RE level precoder cycling. Inother words, the network device may perform precoder cycling on the atleast one spatial stream based on the two different granularities.

In other words, in operation S320, the network device may performprecoder cycling on the at least one transmit diversity spatial streamby using at least one of the following methods:

Method 1:

The network device performs time-frequency resource block based precodercycling on the at least one transmit diversity spatial stream.

Method 2:

The network device performs RE based precoder cycling on the at leastone transmit diversity spatial stream.

Specifically, it is assumed that the network device performs transmitdiversity (for example, the SFTD) preprocessing on the modulated symbolstream to obtain at least two transmit diversity spatial streams, and itis assumed that there are x streams, where x is a natural number greaterthan or equal to 2. In this case, the network device may performprecoder cycling on each of the at least two transmit diversity spatialstreams. For ease of understanding, the following describes method 1 andmethod 2 in detail with reference to FIG. 4 to FIG. 6.

In method 1, the network device may perform time-frequency resourceblock based precoder cycling on the x transmit diversity spatialstreams. On one time-frequency resource block, each transmit diversityspatial stream corresponds to one demodulation reference signal (DMRS)port, the x transmit diversity spatial streams correspond to x DMRSports, and each DMRS port corresponds to one precoding vector on onetime-frequency resource block.

In one embodiment, one time-frequency resource block may include atleast one of the following: a part of one resource element, one resourceelement, or more resource elements. The resource element may beunderstood as a minimum scheduling unit for physical layer transmission.The time-frequency resource block may include at least two REs. In apossible design, one resource element may be one RB. In other words, thetime-frequency resource block may include a part of one RB, one RB, or aplurality of RBs.

Time-frequency resource block based precoding means that a precodinggranularity is a time-frequency resource block. Each DMRS port has oneprecoding vector on one time-frequency resource block, and one DMRS portcorresponds to different precoding vectors on any two consecutivetime-frequency resource blocks. It should be noted that “consecutive”herein may be consecutive in time domain or consecutive in frequencydomain; or the two time-frequency resource blocks are only twotime-frequency resource blocks that are closely neighboring to eachother in a scheduling process, and the two time-frequency resourceblocks are inconsecutive in terms of resource distribution. In addition,different DMRS ports also correspond to different precoding vectors on asame time-frequency resource (or a same time-frequency resource block).The precoding vector may be cyclically used in a cycle of at least twotime-frequency resource blocks. In other words, precoder cycling isperformed in a cycle of at least two time-frequency resource blocks.

In one embodiment, operation S320 includes:

performing, by the network device, time-frequency resource block basedprecoding on each of the at least one transmit diversity spatial streambased on a precoding vector corresponding to the transmit diversityspatial stream on each time-frequency resource block, to obtain the atleast one precoded data stream; or

performing, by the network device, time-frequency resource block basedprecoding on x transmit diversity spatial streams based on a precodingmatrix corresponding to the x transmit diversity spatial streams on eachtime-frequency resource block, where the precoding matrix is combined bycombining x precoding vectors.

It should be noted herein that the time-frequency resource block mayinclude a virtual time-frequency resource block. If each time-frequencyresource block is one RB, the virtual time-frequency resource block maycorrespond to a virtual resource block (VRB) defined in an existingprotocol, and a physical time-frequency resource block may correspond toa physical resource block (PRB) defined in an existing protocol. The anytwo consecutive time-frequency resource blocks may be logicallyconsecutive virtual time-frequency resource blocks, or may be physicallyconsecutive physical time-frequency resource blocks. This embodiment ofthe present invention imposes no special limitation thereto. In thisembodiment of the present invention, an example of using an RB as atime-frequency resource block is used only for ease of understanding,and the precoder cycling is described in detail with reference to theaccompanying drawings.

FIG. 4 is a schematic diagram of time-frequency resource block basedprecoder cycling. Specifically, FIG. 4 is a schematic diagram ofprecoder cycling performed in a granularity of a PRB (in other words, anexample of a time-frequency resource block). As shown in FIG. 4, thereare x transmit diversity spatial streams, and therefore a precodingmatrix corresponding to the x transmit diversity spatial streams on onetime-frequency resource block (in other words, one PRB in thisembodiment) is a precoding matrix obtained by combining x precodingvectors. Therefore, a PRB #1 corresponds to a precoding matrix A, whichmay be, for example, W_(A); and a PRB #2 corresponds to a precodingmatrix B, which may be, for example, W_(B). The precoding matrix A andthe precoding matrix B are two different precoding matrices. For eachtransmit diversity spatial stream, a precoding vector corresponding tothe PRB #1 is also different from a precoding vector corresponding tothe PRB #2.

It is assumed that a quantity x of the at least two spatial streams is2, the two transmit diversity spatial streams may be:

$\begin{bmatrix}s_{1} & {- s_{2}^{*}} \\s_{2} & s_{1}^{*}\end{bmatrix}.$On the PRB #1, a precoding matrix used for precoding the two transmitdiversity spatial streams is a matrix obtained by combining twoprecoding vectors. In other words, W_(A)=[w₁ w₂]. On the PRB #2, aprecoding matrix used for precoding the two transmit diversity spatialstreams is W_(B)=[w₃ w₄] Alternatively, on the PRB #1, each of the twotransmit diversity spatial streams is precoded by using one columnvector in [w₁ w₂]; and on the PRB #2, each of the two transmit diversityspatial streams is precoded by using one column vector in [w₃ w₄].

It should be understood that only an example in which x is equal to 2 isused for description above. However, this should not constitute anylimitation on this embodiment of the present invention. For example, avalue of x may be 1 or greater than 2.

Specifically, when x>2, the precoding matrix used for precoding the atleast two spatial streams is a precoding matrix obtained by combining xprecoding column vectors, in other words, [w₁ w₂ Λ w_(x)] Alternatively,each of the at least two spatial streams is precoded by using one columnvector in [w₁ w₂Λw_(x)] on each PRB.

When x=1, one transmit diversity spatial stream is precoded, thetransmit diversity spatial stream corresponds to one DMRS port, and thetransmit diversity spatial stream is precoded by using one precodingvector.

It should be noted that precoding vectors used by the network device toprecode transmit diversity spatial streams are different on any twoconsecutive time-frequency resource blocks. However, this does not meanthat all time-frequency resource blocks used to carry the transmitdiversity spatial streams correspond to different precoding vectors. Theprecoder cycling may be performed in a cycle of at least twotime-frequency resource blocks. For example, in FIG. 4, twotime-frequency resource blocks may be used as one cycle. In this case,precoding is performed by using the precoding matrix A on the PRB #1,precoding is performed by using the precoding matrix B on the PRB #2,precoding is performed by using the precoding matrix A on a PRB #3,precoding is performed by using the precoding matrix B on a PRB #4, andso on.

It should be further noted that, if the at least one transmit diversityspatial stream is carried on only one time-frequency resource block,time-frequency resource block based precoder cycling is the same asprecoding in the prior art. The network device may precode the at leastone transmit diversity spatial stream by using a precoding matrixcorresponding to the time-frequency resource block.

Through the foregoing precoder cycling, different precoding vectors areused for a same transmit diversity spatial stream on differenttime-frequency resource blocks. When a channel environment changes orestimation is inaccurate, different precoding vectors may be used ondifferent time-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. In addition, transmit diversity preprocessing is performedbefore precoding, so that at least a spatial diversity gain can beobtained by performing spatial transmit diversity on an originalmodulated symbol stream. Therefore, this helps obtain transmit diversitygains in a plurality of dimensions, improves received signal quality,and improves data transmission reliability, so that robustness of acommunications system can be improved.

It should be understood that, only for ease of understanding, an exampleof using one PRB as one time-frequency resource block is used above todescribe time-frequency resource block based precoder cycling in detail.However, this should not constitute any limitation on this embodiment ofthe present invention. The time-frequency resource block may bealternatively an RB group (RBG) including a plurality of RBs. Forexample, the plurality of RBs in the RB group correspond to a sameprecoding matrix, and any two consecutive RB groups correspond todifferent precoding matrices. Alternatively, the time-frequency resourceblock may be a part of one RB, for example, may be a ½ RB, or a ¼ RB. Adefinition of the time-frequency resource block is not specially limitedin this embodiment of the present invention.

It should be noted that, for the foregoing enumerated RB, RBG, PRB, andVRB, refer to definitions in an existing protocol (for example, an LTEprotocol). However, this application does not exclude new definitions ofthe foregoing enumerated RB, RBG, PRB, and VRB in a future protocol, orexclude other names used to replace the foregoing names.

In method 2, the network device performs RE based precoder cycling onthe x transmit diversity spatial stream. In other words, a precodercycling granularity is further refined on one time-frequency resourceblock, so that the time-frequency resource block includes at least twoREs corresponding to different precoding matrices. A precoder cyclingcycle may be one time-frequency resource block, in other words, may beREs whose quantity is an integer multiple of y.

In this precoder cycling method, the network device may perform RE basedprecoding on each of the at least one transmit diversity spatial streambased on the at least two precoding vectors corresponding to thetransmit diversity spatial stream on each time-frequency resource block.To be specific, the network device performs RE based precoding on the xtransmit diversity spatial streams based on y precoding matricescorresponding to the x transmit diversity spatial streams on eachtime-frequency resource block, and each precoding matrix is obtained bycombining x precoding vectors.

Specifically, a correspondence between a quantity of layer-mappingspatial layers and a quantity of DMRS ports may be defined as any one ofthe following:

Definition 1: A quantity of layer-mapping spatial layers may bedifferent from a quantity of DMRS ports corresponding to thelayer-mapping spatial layers.

It is assumed that a quantity of the at least one layer-mapping spatiallayer is x (x≥1, and x is a natural number), and each layer-mappingspatial layer corresponds to y (y≥2, and y is a natural number) DMRSports on one time-frequency resource block. In this case, the xlayer-mapping spatial layers correspond to x×y DMRS ports on thetime-frequency resource block, and correspond to x×y precoding vectors;or the x layer-mapping spatial layers correspond to y precodingmatrices, and each precoding matrix is obtained by combining x precodingvectors.

For example, a quantity x of layer-mapping spatial layers obtained afterlayer mapping is 2, and each layer may correspond to four (in otherwords, y=4) DMRS ports on one time-frequency resource block, in otherwords, correspond to four precoding vectors. In this case, there are twolayer-mapping spatial layers, the two layer-mapping spatial layerscorrespond to eight DMRS ports and eight precoding vectors. In otherwords, one layer corresponds to a plurality of DMRS ports, and each DMRSport corresponds to one precoding vector.

Definition 2: A quantity of layer-mapping spatial layers may be the sameas a quantity of DMRS ports corresponding to the layer-mapping spatiallayers.

It is assumed that a quantity z of the at least one layer-mappingspatial layer is x×y (x≥1, y≥2, and x, y, and z are all naturalnumbers), and each layer-mapping spatial layer corresponds to one DMRSport on one time-frequency resource block. In this case, the x×ylayer-mapping spatial layers correspond to z DMRS ports on thetime-frequency resource block, and correspond to z precoding vectors; orthe x×y layer-mapping spatial layers correspond to y precoding matrices,and each precoding matrix is obtained by combining x precoding vectors.

For example, a quantity z of layer-mapping spatial layers obtained afterlayer mapping is 8, and each layer may correspond to one DMRS port onone time-frequency resource block. In this case, the eight layer-mappingspatial layers correspond to eight DMRS ports and eight precodingvectors. In other words, one layer corresponds to one DMRS port, andeach DMRS port corresponds to one precoding vector.

Definition 3: A quantity of layer-mapping spatial layers may be the sameas a quantity of DMRS ports corresponding to the layer-mapping spatiallayers.

It is assumed that a quantity of the at least one layer-mapping spatiallayer is x (x≥1, and x is a natural number), each layer-mapping spatiallayer corresponds to one DMRS port on one time-frequency resource block,the x layer-mapping spatial layers correspond to x DMRS ports, and eachDMRS port corresponds to y (y≥2, and y is a natural number) precodingvectors. In this case, the x layer-mapping spatial layers correspond tox×y precoding vectors; or the x layer-mapping spatial layers correspondto y precoding matrices, and each precoding matrix is obtained bycombining x precoding vectors.

For example, a quantity x of layer-mapping spatial layers obtained afterlayer mapping is 2, each layer-mapping spatial layer corresponds to oneDMRS port on one time-frequency resource block, and each DMRS portcorrespond to four (y=4) precoding vectors. In this case, there are twolayer-mapping spatial layers, two DMRS ports, and eight precodingvectors. In other words, one layer corresponds to one DMRS port, andeach DMRS port corresponds to a plurality of precoding vectors.

In definition 1 and definition 2, each of the at least one transmitdiversity spatial stream corresponds to at least two DMRS ports on onetime-frequency resource block, and each DMRS port corresponds to oneprecoding vector. For a definition of the DMRS port, refer to adefinition of a DMRS port in an existing protocol (for example, an LTEprotocol). In definition 3, each of the at least one transmit diversityspatial stream corresponds to one DMRS port on one time-frequencyresource block, and each DMRS port corresponds to at least two precodingvectors.

The definition of the DMRS port is slightly different from that of aDMRS port in a current protocol. However, this application does notexclude a possibility of modifying or supplementing the definition ofthe DMRS port in a future protocol. In this design, one DMRS may beunderstood as a group of DMRS ports defined in the current protocol, andeach group corresponds to at least two precoding vectors. In this case,for a definition of the layer, refer to a definition of a layer in anexisting protocol (for example, an LTE protocol).

It should be noted that the foregoing process of mapping a layer-mappingspatial layer to a DMRS port may specifically include: mapping thelayer-mapping spatial layer to a transmit diversity spatial stream, andthen mapping the transmit diversity spatial stream to the DMRS port,where a quantity of transmit diversity spatial streams may be the sameas a quantity of layer-mapping spatial layers.

It should be understood that the quantity of layer-mapping spatiallayers, the quantity of DMRS ports, and the quantity of precodingvectors enumerated above are merely used to describe relationshipsbetween a quantity of layers, a quantity of DMRS ports, and a quantityof precoding vectors in different definitions, and should not constituteany limitation on this embodiment of the present invention.

RE level based precoding means that a precoding granularity is an RE, orRE level based precoding is referred to as RE level precoder cycling. AnRE level indicates that at least two REs in one time-frequency resourceblock correspond to different precoding matrices. It can be understoodthat, for x transmit diversity spatial streams, a precoding matrix is amatrix including x column vectors. When there is one transmit diversityspatial stream, x=1 and there is one precoding vector. For brevity,descriptions of same or similar cases are omitted below. In addition,different transmit diversity spatial streams also correspond todifferent precoding vectors on a same time-frequency resource (forexample, a same RE).

In one embodiment, operation S320 includes:

performing, by the network device, RE based precoding on each of the atleast one transmit diversity spatial stream based on at least twoprecoding vectors corresponding to the transmit diversity spatial streamon each time-frequency resource block, to obtain the at least oneprecoded data stream; or

performing, by the network device, RE based precoding on the x transmitdiversity spatial streams based on y precoding matrices corresponding tothe x transmit diversity spatial streams on each time-frequency resourceblock, where the precoding matrix is obtained by combining x precodingvectors.

FIG. 5 is a schematic diagram of RE based precoder cycling.Specifically, FIG. 5 shows a case in which one time-frequency resourceblock is a part of one PRB. As shown in FIG. 5, on one PRB, twoconsecutive REs in frequency domain may be one RE pair, and any twoconsecutive RE pairs correspond to different precoding matrices.

It should be noted that FIG. 5 is a schematic diagram of a precodingmatrix used to precoding at least two transmit diversity spatial streamsobtained after SFTD preprocessing. After the SFTD, one RE pair occupiestwo contiguous subcarriers in frequency domain, and occupies one symbolin time domain; and precoder cycling is also performed based ondifferent frequency domain resources. On a same frequency domainresource, REs on any two neighboring symbols may use a same precodingvector or different precoding vectors. This embodiment of the presentinvention imposes no special limitation thereto.

In addition, when the transmit diversity preprocessing method is theSFTD, the at least two spatial streams may be obtained. If x=2, theprecoding vector may be cyclically used in a cycle of at least four REs(in other words, at least two RE pairs (RE pair), where each RE pairincludes two REs), or precoder cycling is performed in a cycle of atleast two REs. In other words, a precoder cycling cycle is y RE pairs,and a value of y is 2. Therefore, the time-frequency resource blockshown in FIG. 5 is a ⅓ PRB.

As shown in FIG. 5, there are x transmit diversity spatial streams, andtherefore a precoding matrix corresponding to the x transmit diversityspatial streams on one PRB is a precoding matrix obtained by combining xprecoding vectors. Therefore, an RE pair #1 corresponds to a precodingmatrix A, which may be, for example, W_(A); and an RE pair #2corresponds to a precoding matrix B, which may be, for example, W_(B).The precoding matrix A and the precoding matrix B are two differentprecoding matrices. For each transmit diversity spatial stream, aprecoding vector corresponding to the RE pair #1 is also different froma precoding vector corresponding to the RE pair #2. However, it shouldbe understood that FIG. 5 is a possible schematic diagram of RE levelprecoder cycling shown for ease of understanding, and this should notconstitute any limitation on this embodiment of the present invention.For example, there may be more corresponding precoding matrices on onePRB.

FIG. 6 is another schematic diagram of RE based precoder cycling.Specifically, FIG. 6 shows a case in which one time-frequency resourceblock is one PRB. As shown in FIG. 6, on one PRB, two consecutive REs intime domain may be one RE pair, and the PRB may correspond to threedifferent precoding vectors, that is, three DMRS ports. In other words,y=3, and a precoder cycling cycle is three RE pairs or onetime-frequency resource block. It should be understood that the RE pairmay include neighboring REs only, some neighboring REs, or noneighboring REs. For example, REs of the RE pair may be non-contiguoussubcarriers or may be located on different symbols. In addition,distribution of RE pairs is not limited to a same symbol or a samesubcarrier. For example, one RE pair may be two consecutive REs on onesubcarrier, or may be two inconsecutive REs on one symbol, or may be twoinconsecutive REs on one subcarrier, or may be two REs on differentsubcarriers on different symbols.

It should be further understood that a quantity of RE pairs is notlimited to 2, and the quantity of RE pairs may be determined based on aquantity of spatial streams obtained through transmit diversitypreprocessing. For example, the quantity of RE pairs may be any evennumber such as 4, 6, or 8; or even may be an odd number greater than 1.This embodiment of the present invention imposes no special limitationthereto.

It should be further understood that there may be y correspondingprecoding matrices on one time-frequency resource block during RE levelprecoder cycling. However, cyclically using the y precoding matrices oneach time-frequency resource block is not limited in this embodiment ofthe present invention. FIG. 7 is still another schematic diagram of REbased precoder cycling. Specifically, FIG. 7 shows a case in which onetime-frequency resource block is two PRBs. As shown in FIG. 7, on a PRB#1, RE based precoding may be performed on at least one transmitdiversity spatial stream by separately using a precoding matrix 1, aprecoding matrix 2, a precoding matrix 3, and a precoding matrix 4; andon a PRB #2, RE based precoding may be performed on the at least onetransmit diversity spatial stream by separately using a precoding matrix5, a precoding matrix 6, a precoding matrix 7, and a precoding matrix 8.In other words, a precoder cycling cycle is eight RE pairs (in otherwords, one time-frequency resource block).

It should be understood that the foregoing enumerated time-frequencyresource block based precoder cycling and RE based precoder cycling areonly two possible implementations of the precoder cycling, and shouldnot constitute any limitation on this embodiment of the presentinvention. The network device and the terminal device may pre-negotiatea precoder cycling granularity. In a data transmission process, data isprecoded and demodulated based on the pre-negotiated precoder cyclinggranularity.

Through the foregoing precoder cycling, different precoding vectors areused for a same transmit diversity spatial stream on a sametime-frequency resource block. When a channel environment changes orestimation is inaccurate, different precoding vectors may be used ondifferent time-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. In addition, transmit diversity preprocessing is performedbefore precoding, so that at least a spatial diversity gain can beobtained by performing spatial transmit diversity on an originalmodulated symbol stream. Therefore, this helps obtain transmit diversitygains in a plurality of dimensions, improves received signal quality,and improves data transmission reliability, so that robustness of acommunications system can be improved.

It should be noted that a precoding matrix used in the foregoingprecoder cycling process may be obtained through CSI feedback, or may beobtained based on channel reciprocity, or may be specified by thenetwork device, or even may be determined by using a combination of theforegoing methods. It should be understood that the foregoing enumeratedmethods for determining a precoding matrix by the network device may beimplemented by using a prior art. For brevity, the method fordetermining a precoding matrix is not described in detail herein.

Operation S330. The network device sends the at least one precoded datastream to a first terminal device.

After performing the foregoing processing on the original modulatedsymbol stream, the network device obtains the at least one precoded datastream, and sends the at least one precoded data stream to the firstterminal device. Correspondingly, in operation S330, the first terminaldevice receives the at least one precoded data stream sent by thenetwork device.

A precoding-based transmission process may be briefly represented as thefollowing formula:Y=HWS+n, where

Y represents a vector of a signal received by the first terminal device,H represents a channel matrix, W represents a precoding matrix, Srepresents a vector of at least one spatial stream sent by the networkdevice, and n represents receiver noise. It can be easily learned thatsignal receiving is affected by the receiver noise n. In this embodimentof the present invention, for ease of description, it is assumed thatthe receiver noise is zero, and a signal is transmitted without anerror. Actually, a plurality of solutions are provided to eliminate theforegoing noise in the prior art. For brevity, descriptions of same orsimilar cases are omitted below.

However, it can be understood that the network device may send precodeddata streams to a plurality of terminal devices by using a MU-MIMOtechnology. For example, the network device may send the at least oneprecoded data stream to another one or more terminal devices whilesending the at least one precoded data stream to the first terminaldevice. A transmission scheme for a precoded data stream correspondingto each terminal device may be transmit diversity, precoder cycling,spatial multiplexing, or the like. This embodiment of the presentinvention imposes no special limitation thereto.

In one embodiment, the at least one transmit diversity spatial stream isa spatial stream corresponding to the first terminal device in aplurality of spatial streams, and the plurality of spatial streamscorrespond to a plurality of terminal devices including the firstterminal device.

In this embodiment of the present invention, the plurality of spatialstreams correspond to the plurality of terminal devices, and it can beunderstood that the plurality of spatial streams are sent to theplurality of terminal devices. For example, the at least one transmitdiversity spatial stream may be a spatial stream sent to the firstterminal device. However, it does not indicate that the at least onetransmit diversity spatial stream is directly sent to the first terminaldevice, and the at least one transmit diversity spatial stream may besent to the first terminal device after other data processing. Forexample, in this embodiment of the present invention, the dataprocessing process may be precoder cycling. However, it should beunderstood that the data processing process is not limited to precodercycling. For example, the data processing process may be another dataprocessing process such as precoding. This embodiment of the presentinvention imposes no special limitation thereto. For brevity,descriptions of same or similar cases are omitted below.

The plurality of spatial streams may be understood as symbol streamsbefore precoding, in other words, layer-mapping spatial layers obtainedafter layer mapping or transmit diversity spatial streams obtained aftera transmit diversity operation. A specific form is related to atransmission scheme used by the spatial stream. In this embodiment ofthe present invention, the spatial stream may make a general referenceof a symbol stream obtained through modulation.

In addition, transmission schemes for the plurality of spatial streamsmay be the same. In other words, the transmission schemes are allprecoder cycling based transmit diversity.

Alternatively, the plurality of spatial streams belong to at least twodifferent transmission schemes.

In one embodiment, at least one of the plurality of spatial streamscorresponds to a second terminal device, and a transmission scheme forthe at least one spatial stream is precoder cycling based transmitdiversity.

FIG. 8 is a schematic diagram in which the network device separatelysends a plurality of spatial streams to the first terminal device andthe second terminal device according to an embodiment of the presentinvention. As shown in FIG. 8, the network device separately sends datato the first terminal device and the second terminal device by using asame time-frequency resource and a same transmission scheme. Thetransmission scheme may be precoder cycling based transmit diversity,and a precoder cycling granularity may be an RE.

In one embodiment, at least one of the plurality of spatial streamscorresponds to a third terminal device, and a transmission scheme forthe at least one spatial stream is spatial multiplexing.

By way of example but not limitation, the spatial multiplexing includesclosed-loop spatial multiplexing (CLSM).

FIG. 9 is a schematic diagram in which the network device separatelysends a plurality of spatial streams to the first terminal device andthe third terminal device according to an embodiment of the presentinvention. As shown in FIG. 9, the network device separately sends datato the first terminal device and the third terminal device by using asame time-frequency resource and different transmission schemes. Atransmission scheme used for data corresponding to the first terminaldevice may be precoder cycling based transmit diversity, a precodercycling granularity is an RE level, and a transmission scheme used fordata corresponding to the third terminal device is spatial multiplexing.

In one embodiment, at least one of the plurality of spatial streamscorresponds to a fourth terminal device, and a transmission scheme forthe at least one spatial stream is transmit diversity.

By way of example but not limitation, the transmit diversity includesdiversity manners such as space time transmit diversity (STTD), aspace-frequency transmit diversity (SFTD), a time switched transmitdiversity (TSTD), frequency switched transmit diversity (FSTD),orthogonal transmit diversity (OTD), cyclic delay diversity (CDD), andlayer shifting, diversity manners obtained after derivation, evolution,and combination of the foregoing various diversity manners, and spatialmultiplexing performed based on the foregoing enumerated transmitdiversity manners.

In one embodiment, at least one of the plurality of spatial streamscorresponds to a fifth terminal device, and a transmission scheme forthe at least one spatial stream is precoder cycling.

It should be understood that FIG. 8 and FIG. 9 are only schematicdiagrams, shown for ease of understanding, in which the network devicesends data to a plurality of terminal devices. However, this should notconstitute any limitation on this embodiment of the present invention.The network device may send data to more terminal devices, and thenetwork device may send the data to the more terminal devices by usingone or more transmission schemes. This embodiment of the presentinvention imposes no special limitation thereto.

Operation S340. The first terminal device demodulates the at least oneprecoded data stream to obtain an estimated value of the modulatedsymbol stream.

After receiving the at least one precoded data stream, the firstterminal device may demodulate the at least one precoded data streambased on an inverse process of operations S310 and S320 to obtain theestimated value of the original modulated symbol stream.

In one embodiment, operation S340 includes:

obtaining, by the first terminal device, an estimated value of at leastone layer-mapping spatial layer from the at least one precoded datastream through demodulation; and

performing, by the first terminal device, inverse layer mapping on theestimated value of the at least one layer-mapping spatial layer toobtain the estimated value of the modulated symbol stream.

First, for a received signal Y, the first terminal device may determinean equivalent channel matrix HW based on a DMRS, and obtains theestimated value of the at least one layer-mapping spatial layer throughdemodulation. It can be understood that the estimated value of the atleast one layer-mapping spatial layer corresponds to at least onelayer-mapping spatial layer obtained by the network device by performinglayer mapping on the original modulated symbol stream.

It is assumed that the receiver noise is zero, and a vector r of asignal that is obtained by the first terminal device throughdemodulation and that is sent to the first terminal device may berepresented as follows:

${r = {{{HW}_{i}S_{i}} + {\sum\limits_{j \neq i}{{HW}_{j}S_{j}}}}},$where

H represents a channel matrix used by the network device to send data tothe first terminal device, W_(i) represents a precoding matrix of a datastream sent to the first terminal device, and W_(j) represents aprecoding matrix of a data stream sent to another terminal device (forexample, any one or more of the second terminal device to the fifthterminal device).

The first terminal device may process the received signal by usingvarious receiving algorithms, so that interference is zero.Specifically, the first terminal device may design each column vector,in the precoding matrix W_(j) of the at least one spatial stream sent toanother terminal device, to be orthogonal to each row vector in H, sothat

$\sum\limits_{j \neq i}{{HW}_{j}S_{j}}$is zero. In other words, the interference is zero. Therefore, the firstterminal device may estimate the equivalent channel matrix based on areceived DMRS sent to the first terminal device, and obtain, throughdemodulation based on the estimated equivalent channel matrix HW_(i), alayer-mapping spatial layer sent by the network device to the firstterminal device (it can be understood that the layer-mapping spatiallayer herein is estimated, namely, the estimated value of thelayer-mapping spatial layer).

It should be noted that the network device performs transmit diversitypreprocessing, for example, SFTD, on the original modulated symbolstream to obtain the at least one transmit diversity spatial stream, andprecodes the at least one transmit diversity spatial stream by using aprecoder cycling method. Therefore, the network device needs todemodulate a received signal based on different REs or precoding vectorscorresponding to different RBs.

Because the network device precodes the transmit diversity spatialstream by using the precoder cycling method, there are at least twoprecoding vectors used for each transmit diversity spatial stream, andthere are also at least two equivalent channel matrices corresponding toeach precoded data stream. Therefore, the first terminal device maydemodulate the at least one precoded data stream based on differentequivalent channel matrices estimated by using different DMRSs.

Specifically, in operation S340, considering that a channel matrix maychange in time domain and/or in frequency domain, the first terminaldevice may demodulate the at least one precoded data stream based on anequivalent channel matrix corresponding to each RE, and the equivalentchannel matrix corresponding to each RE may be obtained through estimateinterpolation based on a corresponding DMRS port.

In operation S320, the precoder cycling may be time-frequency resourceblock based precoder cycling, or may be RE based precoder cycling. Ifthe precoder cycling is the time-frequency resource block based precodercycling, in operation S340, an equivalent channel matrix correspondingto each RE on one time-frequency resource block may be obtained throughestimate interpolation based on one corresponding DMRS port. If theprecoder cycling is the RE based precoder cycling, in S340, anequivalent channel matrix corresponding to each RE on one time-frequencyresource block may be obtained through estimate interpolation based oncorresponding DMRS ports, and there are at least two corresponding DMRSports on the time-frequency resource block.

Regardless of whether the precoder cycling granularity is atime-frequency resource block or an RE, during demodulation processing,the equivalent channel matrix needs to be estimated based on a DMRS portcorresponding to each RE.

For example, if a transmit diversity preprocessing manner is SFTD, andthere are two streams, for same time-frequency resource blocks (whichcorrespond to the time-frequency resource block based precoder cycling)having a same precoding vector, or for a same RE pair (which correspondsto the RE level precoder cycling), an equivalent channel matrixestimated based on two DMRSs is as follows:

$H_{eff} = {\begin{bmatrix}h_{11} & h_{12} \\h_{22}^{*} & {- h_{21}^{*}}\end{bmatrix}.}$

In this case, estimated values

$\begin{bmatrix}{\overset{\sim}{s}}_{1} \\{\overset{\sim}{s}}_{2}\end{bmatrix}\quad$of the at least two layer-mapping spatial layers may be simultaneouslyobtained through demodulation.

Herein, {tilde over (s)} represents an estimated value of s, hrepresents an equivalent channel matrix corresponding to a DMRS port,h₁₁ represents an equivalent channel vector estimated by using a firstDMRS port of a first RE, h₁₂ represents an equivalent channel vectorestimated by using a second DMRS port of the first RE, h₂₁ represents anequivalent channel vector estimated by using a first DMRS port of asecond RE, h₂₂ represents an equivalent channel vector estimated byusing a second DMRS port of the second RE, and h* represents a conjugateof h.

If equivalent channels of same DMRS ports on two neighboring REs areaveraged, a channel difference between REs may be ignored, and theforegoing equivalent channel matrix may be simplified as follows:

${H_{eff} = \begin{bmatrix}h_{1} & h_{2} \\h_{2}^{*} & {- h_{1}^{*}}\end{bmatrix}},$

where

h₁ represents an equivalent channel vector corresponding to a first DMRSport, and h₂ represents an equivalent channel vector corresponding to asecond DMRS port.

Then the first terminal device performs inverse layer mapping on theestimated value of the at least one layer-mapping spatial layer toobtain the estimated value of the original modulated symbol stream.

Specifically, the first terminal device may perform inverse layermapping on estimated values of two layer-mapping spatial layers obtainedthrough demodulation, to obtain the estimated value of the originalmodulated symbol stream. Then the modulated symbol stream is input to adecoder for decoding, to obtain an estimated value of a data bit. Ifcyclic redundancy check (cyclic redundancy check, CRC) succeeds, it isdetermined that the estimated value of the data bit is the same as thatof an original data bit.

It should be understood that, for a specific data demodulation process,refer to the transmit diversity transmission scheme and the precodercycling transmission scheme in the prior art. For brevity, detaileddescriptions of specific processes are omitted herein. Therefore,transmit diversity preprocessing is performed before precoding, so thatat least a spatial diversity gain can be obtained by performing spatialtransmit diversity on an original modulated symbol stream. In addition,precoder cycling is performed on a spatial stream obtained aftertransmit diversity preprocessing, so that different precoding vectorsare used for a same transmit diversity spatial stream. When a channelenvironment changes or a channel is inaccurately estimated, differentprecoding vectors may be used on different time-frequency resources forchannel matching, and at least a time-domain diversity gain or afrequency-domain diversity gain may be obtained. Therefore, this helpsobtain transmit diversity gains in a plurality of dimensions, improvesreceived signal quality, and improves data transmission reliability, sothat robustness of a communications system can be improved.

FIG. 10 is a schematic flowchart of a data transmission method 400according to another embodiment of the present invention from aperspective of device interaction. Specifically, FIG. 10 shows an uplinkdata transmission process.

As shown in FIG. 10, the method 400 includes the following operations.

Operation S410. A first terminal device performs transmit diversitypreprocessing on one modulated symbol stream to obtain at least onetransmit diversity spatial stream.

Operation S420. The first terminal device performs precoder cycling onthe at least one transmit diversity spatial stream to obtain at leastone precoded data stream.

Operation S430. The first terminal device sends the at least oneprecoded data stream to a network device.

Operation S440. A second terminal device sends at least one precodeddata stream to the network device.

In operations S430 and S440, the network device receives a plurality ofprecoded data streams sent by the first terminal device and the secondterminal device.

Operation S450. The network device demodulates the plurality of precodeddata streams to obtain estimated values of a plurality of modulatedsymbol streams.

It should be understood that a specific process in which the firstterminal device sends uplink data to the network device is similar to aspecific process in which the network device sends downlink data to thefirst terminal device. The foregoing describes the specific downlinktransmission process in detail with reference to operations S310 toS340. For brevity, detailed descriptions of uplink transmission inoperations S410 to S450 are omitted herein.

It should be further understood that the foregoing description withreference to FIG. 10 is merely an example, and should not constitute anylimitation on this embodiment of the present invention. For example, thenetwork device may further simultaneously receive precoded data streamssent by more terminal devices. In other words, a plurality of precodeddata streams received by the network device may correspond to aplurality of terminal devices including the first terminal device. Inone embodiment, the plurality of terminal devices include the secondterminal device. In one embodiment, during uplink transmission, theplurality of terminal devices may send, through spatial multiplexing,data to one network device by using a same time-frequency resource, andthe plurality of terminal devices may use a same transmission scheme, ormay use at least two different transmission schemes.

Therefore, transmit diversity preprocessing is performed beforeprecoding, so that at least a spatial diversity gain can be obtained byperforming spatial transmit diversity on an original modulated symbolstream. In addition, precoder cycling is performed on a spatial streamobtained after transmit diversity preprocessing, so that differentprecoding vectors are used for a same transmit diversity spatial stream.When a channel environment changes or a channel is inaccuratelyestimated, different precoding vectors may be used on differenttime-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. Therefore, this helps obtain transmit diversity gains in aplurality of dimensions, improves received signal quality, and improvesdata transmission reliability, so that robustness of a communicationssystem can be improved.

FIG. 11 is a schematic block diagram of a network device 10 according toan embodiment of the present invention. As shown in FIG. 11, the networkdevice 10 includes a processing module 11 and a sending module 12.

Specifically, the network device 10 may correspond to the network devicein the data transmission method 300 according to the embodiment of thepresent invention. The network device 10 may include modules configuredto perform the method performed by the network device in the datatransmission method 300 in FIG. 3. In addition, the modules in thenetwork device 10 and the foregoing other operations and/or functionsare respectively intended to implement corresponding procedures of thedata transmission method 300 in FIG. 3. For brevity, details are notdescribed herein.

FIG. 12 is a schematic block diagram of a terminal device 20 accordingto an embodiment of the present invention. As shown in FIG. 12, theterminal device 20 includes a receiving module 21 and a processingmodule 22.

Specifically, the terminal device 20 may correspond to the firstterminal device in the data transmission method 300 according to theembodiment of the present invention. The terminal device 20 may includemodules configured to perform the method performed by the first terminaldevice in the data transmission method 300 in FIG. 3. In addition, themodules in the terminal device 20 and the foregoing other operationsand/or functions are respectively intended to implement correspondingprocedures of the data transmission method 300 in FIG. 3. For brevity,details are not described herein.

FIG. 13 is a schematic block diagram of a terminal device 30 accordingto another embodiment of the present invention. As shown in FIG. 13, theterminal device 30 includes a processing module 31 and a sending module32.

The processing module 31 is configured to: perform transmit diversitypreprocessing on one modulated symbol stream to obtain at least onetransmit diversity spatial stream; and perform precoder cycling on theat least one transmit diversity spatial stream to obtain at least oneprecoded data stream, where each of the at least one transmit diversityspatial stream corresponds to at least two different precoding vectors.

The sending module 32 is configured to send the at least one precodeddata stream to a network device.

In one embodiment, the processing module 31 is specifically configuredto:

perform layer mapping on the modulated symbol stream to obtain at leastone layer-mapping spatial layer; and

perform a transmit diversity operation on the at least one layer-mappingspatial layer to obtain the at least one transmit diversity spatialstream.

In one embodiment, the precoder cycling includes time-frequency resourceblock based precoder cycling, each of the at least one transmitdiversity spatial stream corresponds to one precoding vector on onetime-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.

In one embodiment, the precoder cycling includes resource element (RE)based precoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.

Specifically, the terminal device 30 may correspond to the firstterminal device in the data transmission method 400 according to theembodiment of the present invention. The terminal device 30 may includemodules configured to perform the method performed by the first terminaldevice in the data transmission method 400 in FIG. 10. In addition, themodules in the terminal device 30 and the foregoing other operationsand/or functions are respectively intended to implement correspondingprocedures of the data transmission method 400 in FIG. 10. For brevity,details are not described herein.

FIG. 14 is a schematic block diagram of a network device 40 according toanother embodiment of the present invention. As shown in FIG. 14, thenetwork device includes a receiving module 41 and a processing module42.

The receiving module 41 is configured to receive at least one precodeddata stream sent by a first terminal device, where the at least oneprecoded data stream is obtained by the first terminal device byperforming precoder cycling on at least one transmit diversity spatialstream, the at least one transmit diversity spatial stream is obtainedby performing transmit diversity preprocessing based on one modulatedsymbol stream, and each of the at least one transmit diversity spatialstream corresponds to at least two different precoding vectors.

The processing module 42 is configured to demodulate the at least oneprecoded data stream to obtain an estimated value of the modulatedsymbol stream.

In one embodiment, the processing module 42 is specifically configuredto:

obtain an estimated value of at least one layer-mapping spatial layerfrom the at least one precoded data stream through demodulation, wherethe estimated value of the at least one layer-mapping spatial layercorresponds to at least one layer-mapping spatial layer obtained by thenetwork device by performing layer mapping on the modulated symbolstream; and

perform inverse layer mapping on the estimated value of the at least onelayer-mapping spatial layer to obtain the estimated value of themodulated symbol stream.

In one embodiment, the precoder cycling includes time-frequency resourceblock based precoder cycling, each of the at least one transmitdiversity spatial stream corresponds to one precoding vector on onetime-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.

In one embodiment, the precoder cycling includes resource element (RE)based precoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.

In one embodiment, the at least one transmit diversity spatial stream isa spatial stream corresponding to the first terminal device in aplurality of spatial streams, and the plurality of spatial streamscorrespond to a plurality of terminal devices including the firstterminal device.

In one embodiment, transmission schemes for the plurality of spatialstreams are the same.

In one embodiment, the plurality of spatial streams belong to at leasttwo transmission schemes.

In one embodiment, the at least two transmission schemes includeprecoder cycling, transmit diversity, spatial multiplexing, or precodercycling based transmit diversity.

Specifically, the network device 40 may correspond to the network devicein the data transmission method 400 according to the embodiment of thepresent invention. The network device 40 may include modules configuredto perform the method performed by the network device in the datatransmission method 400 in FIG. 10. In addition, the modules in thenetwork device 40 and the foregoing other operations and/or functionsare respectively intended to implement corresponding procedures of thedata transmission method 400 in FIG. 10. For brevity, details are notdescribed herein.

Therefore, transmit diversity preprocessing is performed beforeprecoding, so that at least a spatial diversity gain can be obtained byperforming spatial transmit diversity on an original modulated symbolstream. In addition, precoder cycling is performed on a spatial streamobtained after transmit diversity preprocessing, so that differentprecoding vectors are used for a same transmit diversity spatial stream.When a channel environment changes or a channel is inaccuratelyestimated, different precoding vectors may be used on differenttime-frequency resources for channel matching, and at least atime-domain diversity gain or a frequency-domain diversity gain may beobtained. Therefore, this helps obtain transmit diversity gains in aplurality of dimensions, improves received signal quality, and improvesdata transmission reliability, so that robustness of a communicationssystem can be improved.

FIG. 15 is a schematic block diagram of a network device 50 according toan embodiment of the present invention. As shown in FIG. 15, the networkdevice 50 includes a transceiver 51, a processor 52, and a memory 53.The transceiver 51, the processor 52, and the memory 53 communicate witheach other by using an internal connection path to transfer a controlsignal and/or a data signal. The memory 53 is configured to store acomputer program, and the processor 52 is configured to invoke thecomputer program from the memory 53 and run the computer program tocontrol the transceiver 51 to receive and send a signal. The memory 53may be disposed in the processor 52, or may be independent of theprocessor 52.

Specifically, the network device 50 may correspond to the network devicein the data transmission method 300 according to the embodiment of thepresent invention. The network device 50 may include units configured toperform the method performed by the network device in the datatransmission method 300 in FIG. 3. In addition, the units in the networkdevice 50 and the foregoing other operations and/or functions arerespectively intended to implement corresponding procedures of the datatransmission method 300 in FIG. 3. For brevity, details are notdescribed herein.

Alternatively, the network device 50 may correspond to the networkdevice in the data transmission method 400 according to the embodimentof the present invention. The network device 50 may include unitsconfigured to perform the method performed by the network device in thedata transmission method 400 in FIG. 10. In addition, the units in thenetwork device 50 and the foregoing other operations and/or functionsare respectively intended to implement corresponding procedures of thedata transmission method 400 in FIG. 10. For brevity, details are notdescribed herein.

FIG. 16 is a schematic block diagram of a terminal device 60 accordingto an embodiment of the present invention. As shown in FIG. 16, theterminal device 60 includes a transceiver 61, a processor 62, and amemory 63. The transceiver 61, the processor 62, and the memory 63communicate with each other by using an internal connection path totransfer a control signal and/or a data signal. The memory 63 isconfigured to store a computer program, and the processor 62 isconfigured to invoke the computer program from the memory 63 and run thecomputer program to control the transceiver 61 to receive and send asignal. The memory 63 may be disposed in the processor 62, or may beindependent of the processor 62.

Specifically, the terminal device 60 may correspond to the firstterminal device in the data transmission method 300 according to theembodiment of the present invention. The terminal device 60 may includeunits configured to perform the method performed by the first terminaldevice in the data transmission method 300 in FIG. 3. In addition, theunits in the terminal device 60 and the foregoing other operationsand/or functions are respectively intended to implement correspondingprocedures of the data transmission method 300 in FIG. 3. For brevity,details are not described herein.

Alternatively, the terminal device 60 may correspond to the firstterminal device in the data transmission method 400 according to theembodiment of the present invention. The terminal device 60 may includeunits configured to perform the method performed by the first terminaldevice in the data transmission method 400 in FIG. 10. In addition, theunits in the terminal device 60 and the foregoing other operationsand/or functions are respectively intended to implement correspondingprocedures of the data transmission method 400 in FIG. 10. For brevity,details are not described herein.

It should be understood that, in the embodiments of the presentinvention, the processor may be a central processing unit (CPU); or theprocessor may be another general-purpose processor, a digital signalprocessor (DSP), an application-specific integrated circuit (ASIC), afield programmable gate array (FPGA) or another programmable logicdevice, a discrete gate or transistor logic device, a discrete hardwarecomponent, or the like.

It should be further understood that the memory in the embodiments ofthe present invention may be a volatile memory or a nonvolatile memory,or may include a volatile memory and a nonvolatile memory. Thenonvolatile memory may be a read-only memory (ROM), a programmableread-only memory (PROM), an erasable programmable read-only memory(EPROM), an electrically erasable programmable read-only memory(EEPROM), or a flash memory. The volatile memory may be a random accessmemory (RAM) serving as an external cache. By way of example but notlimitation, many forms of random access memories (RAM) may be used, forexample, a static random access memory (SRAM), a dynamic random accessmemory (DRAM), a synchronous dynamic random access memory (SDRAM), adouble data rate synchronous dynamic random access memory (DDR SDRAM),an enhanced synchronous dynamic random access memory (ESDRAM), asynchlink dynamic random access memory (SLDRAM), and a direct rambusrandom access memory (DR RAM).

All or some of the foregoing embodiments may be implemented throughsoftware, hardware, firmware, or any combination thereof. When thesoftware is used to implement the embodiments, all or some of theembodiments may be implemented in a form of a computer program product.The computer program product includes one or more computer instructions.When the computer program instructions are loaded or executed on acomputer, the procedures or functions according to the embodiments ofthe present invention are all or partially generated. The computer maybe a general-purpose computer, a dedicated computer, a computer network,or another programmable apparatus. The computer instructions may bestored in a computer readable storage medium, or may be transmitted froma computer readable storage medium to another computer readable storagemedium. For example, the computer instructions may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, infrared, radio, ormicrowave) manner. The computer readable storage medium may be anyusable medium accessible by a computer, or a data storage device, suchas a server or a data center, integrating one or more usable media. Theusable medium may be a magnetic medium (for example, a floppy disk, ahard disk, or a magnetic tape), an optical medium (for example, a DVD),or a semiconductor medium. The semiconductor medium may be a solid-statedrive.

It should be understood that the term “and/or” in this specificationdescribes only an association relationship for describing associatedobjects and represents that three relationships may exist. For example,A and/or B may represent the following three cases: Only A exists, bothA and B exist, and only B exists. In addition, the character “/” in thisspecification generally indicates an “or” relationship between theassociated objects.

It should be understood that sequence numbers of the foregoing processesdo not mean execution sequences in various embodiments of thisapplication. The execution sequences of the processes should bedetermined according to functions and internal logic of the processes,and should not be construed as any limitation on the implementationprocesses of the embodiments of this application.

A person of ordinary skill in the art may be aware that, the units andalgorithm operations in the examples described with reference to theembodiments disclosed in this specification may be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraints of thetechnical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of this application.

It can be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments, anddetails are not described herein again.

In the several embodiments provided in this application, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiment is merely an example. For example, the unit division ismerely logical function division and may be other division during actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented through some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electrical, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected based on actualrequirements to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of this application maybe integrated into one processing unit, or each of the units may existalone physically, or two or more units are integrated into one unit.

When the functions are implemented in a form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer readable storage medium. Based on such anunderstanding, the technical solutions of this application essentially,or the part contributing to the prior art, or some of the technicalsolutions may be implemented in a form of a software product. Thecomputer software product is stored in a storage medium, and includesseveral instructions for instructing a computer device (which may be apersonal computer, a server, a network device, or the like) to performall or some of the operations of the methods described in theembodiments of this application. The foregoing storage medium includesany medium that can store program code, such as a USB flash drive, aremovable hard disk, a read-only memory (ROM), a random access memory(RAM), a magnetic disk, or an optical disc.

The foregoing descriptions are merely specific implementations of thisapplication, but are not intended to limit the protection scope of thisapplication. Any variation or replacement readily figured out by aperson skilled in the art within the technical scope disclosed in thisapplication should fall within the protection scope of this application.Therefore, the protection scope of this application shall be subject tothe protection scope of the claims.

What is claimed is:
 1. A data sending method, comprising: performing, bya network device, transmit diversity preprocessing on one modulatedsymbol stream to obtain at least one transmit diversity spatial stream;performing, by the network device, precoder cycling on the at least onetransmit diversity spatial stream to obtain at least one precoded datastream, wherein each of the at least one transmit diversity spatialstream corresponds to at least two precoding vectors; and sending, bythe network device, the at least one precoded data stream to a firstterminal device.
 2. The method according to claim 1, wherein theperforming, by a network device, transmit diversity preprocessing on onemodulated symbol stream to obtain at least one transmit diversityspatial stream comprises: performing, by the network device, layermapping on the modulated symbol stream to obtain at least onelayer-mapping spatial layer; and performing, by the network device, atransmit diversity operation on the at least one layer-mapping spatiallayer to obtain the at least one transmit diversity spatial stream. 3.The method according to claim 1, wherein the precoder cycling comprisestime-frequency resource block based precoder cycling, wherein each ofthe at least one transmit diversity spatial stream corresponds to oneprecoding vector on one time-frequency resource block, and each transmitdiversity spatial stream corresponds to different precoding vectors onany two consecutive time-frequency resource blocks.
 4. The methodaccording to claim 1, wherein the precoder cycling comprises resourceelement (RE) based precoder cycling, and each of the at least onetransmit diversity spatial stream corresponds to at least two precodingvectors on one time-frequency resource block.
 5. The method according toclaim 1, wherein the at least one transmit diversity spatial stream is aspatial stream corresponding to the first terminal device in a pluralityof spatial streams, and the plurality of spatial streams correspond to aplurality of terminal devices comprising the first terminal device. 6.The method according to claim 5, wherein the plurality of spatialstreams belong to at least two transmission schemes.
 7. A data receivingmethod, comprising: receiving, by a first terminal device, at least oneprecoded data stream sent by a network device, wherein the at least oneprecoded data stream is obtained by the network device by performingprecoder cycling on at least one transmit diversity spatial stream, theat least one transmit diversity spatial stream is obtained by thenetwork device by performing transmit diversity preprocessing based onone modulated symbol stream, and each of the at least one transmitdiversity spatial stream corresponds to at least two different precodingvectors; and demodulating, by the first terminal device, the at leastone precoded data stream to obtain an estimated value of the modulatedsymbol stream.
 8. The method according to claim 7, wherein thedemodulating, by the first terminal device, the at least one precodeddata stream to obtain an estimated value of the modulated symbol streamcomprises: obtaining, by the first terminal device, an estimated valueof at least one layer-mapping spatial layer from the at least oneprecoded data stream through demodulation, wherein the estimated valueof the at least one layer-mapping spatial layer corresponds to at leastone layer-mapping spatial layer obtained by the network device byperforming layer mapping on the modulated symbol stream; and performing,by the first terminal device, inverse layer mapping on the estimatedvalue of the at least one layer-mapping spatial layer to obtain theestimated value of the modulated symbol stream.
 9. The method accordingto claim 7, wherein the precoder cycling comprises time-frequencyresource block based precoder cycling, wherein each of the at least onetransmit diversity spatial stream corresponds to one precoding vector onone time-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.
 10. The method according to claim 7,wherein the precoder cycling comprises resource element (RE) basedprecoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.
 11. A network device, comprising: aprocessor, configured to: perform transmit diversity preprocessing onone modulated symbol stream to obtain at least one transmit diversityspatial stream; and perform precoder cycling on the at least onetransmit diversity spatial stream to obtain at least one precoded datastream, wherein each of the at least one transmit diversity spatialstream corresponds to at least two different precoding vectors; and atransceiver, configured to send the at least one precoded data stream toa first terminal device.
 12. The network device according to claim 11,wherein the processor is configured to: perform layer mapping on themodulated symbol stream to obtain at least one layer-mapping spatiallayer; and perform a transmit diversity operation on the at least onelayer-mapping spatial layer to obtain the at least one transmitdiversity spatial stream.
 13. The network device according to claim 11,wherein the precoder cycling comprises time-frequency resource blockbased precoder cycling, wherein each of the at least one transmitdiversity spatial stream corresponds to one precoding vector on onetime-frequency resource block, and each transmit diversity spatialstream corresponds to different precoding vectors on any two consecutivetime-frequency resource blocks.
 14. The network device according toclaim 11, wherein the precoder cycling comprises resource element (RE)based precoder cycling, and each of the at least one transmit diversityspatial stream corresponds to at least two precoding vectors on onetime-frequency resource block.
 15. The network device according to claim11, wherein the at least one transmit diversity spatial stream is aspatial stream corresponding to the first terminal device in a pluralityof spatial streams, and the plurality of spatial streams correspond to aplurality of terminal devices comprising the first terminal device. 16.The network device according to claim 15, wherein the plurality ofspatial streams belong to at least two transmission schemes.
 17. Aterminal device, comprising: a transceiver, configured to receive atleast one precoded data stream sent by a network device, wherein the atleast one precoded data stream is obtained by the network device byperforming precoder cycling on at least one transmit diversity spatialstream, the at least one transmit diversity spatial stream is obtainedby the network device by performing transmit diversity preprocessingbased on one modulated symbol stream, and each of the at least onetransmit diversity spatial stream corresponds to at least two differentprecoding vectors; and a processor, configured to demodulate the atleast one precoded data stream to obtain an estimated value of themodulated symbol stream.
 18. The terminal device according to claim 17,wherein the processor is configured to: obtain an estimated value of atleast one layer-mapping spatial layer from the at least one precodeddata stream through demodulation, wherein the estimated value of the atleast one layer-mapping spatial layer corresponds to at least onelayer-mapping spatial layer obtained by the network device by performinglayer mapping on the modulated symbol stream; and perform inverse layermapping on the estimated value of the at least one layer-mapping spatiallayer to obtain the estimated value of the modulated symbol stream. 19.The terminal device according to claim 17, wherein the precoder cyclingcomprises time-frequency resource block based precoder cycling, whereineach of the at least one transmit diversity spatial stream correspondsto one precoding vector on one time-frequency resource block, and eachtransmit diversity spatial stream corresponds to different precodingvectors on any two consecutive time-frequency resource blocks.
 20. Theterminal device according to claim 17, wherein the precoder cyclingcomprises resource element (RE) based precoder cycling, and each of theat least one transmit diversity spatial stream corresponds to at leasttwo precoding vectors on one time-frequency resource block.